2015 MBP - 2.5Ghz, or 2.8Ghz?

[Hoff]

So I'm definitely buying a 2015 MBP. That part is non-negotiable : )

Just wondering which processor you would recommend.

I will rule out the 2.2Ghz straight away.

I do 3D modeling (wants highest single-core speed possible)
And photo-rendering (wants fast speeds, many cores, running 100% on all cores for days at a time)
And probably will do video editing later.

Should I get a 2.5Ghz or 2.8? Is there much difference?

I'm happy to pay the ~$200 extra to go up to 2.8Ghz.
(If it's actually better)

Main question = under constant load, is the 2.8 more likely to get hotter and throttle down anyway? Making the 2.5 basically just as good performance for lower price?

2nd question = does the 2.8Ghz processor introduce any other problems compared to the 2.5Ghz that I'm not aware of? Or vice versa? Thanks

 

[Darmok N Jalad]

The CPUs in the 2.5 and 2.8 are the i7-4870HQ and the i7-4980HQ, respectively. Both are 4-core/8-thread 47W CPUs, so they would require the same cooling (so one shouldn't run any warmer than the other). According to Intel, the 4870HQ boosts to 3.70GHz, while the 4980HQ boosts to 4.00GHz. The GPU also boosts slightly higher on the 4980HQ, but probably not so much that you'll notice.

https://ark.intel.com/compare/83503,83504

So, in the end, the 2.8GHz model is going to be a good buy, especially if you want the fastest max single core speed. I think either CPU is going to throttle down under constant load as the cooling system reaches its limits. I suspect the 4980HQ will still run at a higher overall speed because it's a better bin and should be more capable of maintaining higher clocks. You won't see the boost speed from either for a sustained amount of time.

 

[organicCPU]

By the time of writing my 2015 15" MBP 2.8 GHz is for 1 year and 3 month almost 24h/7d in use without noteworthy problems. If rendering images (Blender in my case), the fans are running loud all the time, but temperature seems to be o.k.. I didn't notice significant throttling, though never kept an eye on this. How would you measure or track this?

Keep in mind that the models that you can still buy at the Apple Store don't have a dedicated GPU (AMD Radeon R9 M370X), just the Intel® Iris™ Pro Graphics 5200. I guess it's quite impossible to get a new unused MJLU2D/A model with dGPU right now. Check out that all the features you need are supported without dGPU. E.g. in Photoshop I don't get some options, if I only use the Iris Pro.

In comparison the 2.8 GHz model is of course faster than the 2.5 GHz, but it just seems around 10 - 20% at single core. https://browser.geekbench.com/v4/cpu/search?dir=desc&q=mid+2015&sort=score

 

[Darmok N Jalad]

How would you measure or track this?

Try the Intel Power Gadget. When I load my i5-7500, which has a base clock of 3.4GHz, it usually sits around 3.6GHz with all 4 cores at 100%. Random bursts seem to shoot up to 3.7GHz. It's rated as a max boost of 3.8GHz, but I believe it only gets that high in very brief bursts.
https://software.intel.com/en-us/articles/intel-power-gadget-20

 

[Hoff]

The CPUs in the 2.5 and 2.8 are the i7-4870HQ and the i7-4980HQ, respectively. Both are 4-core/8-thread 47W CPUs, so they would require the same cooling (so one shouldn't run any warmer than the other). According to Intel, the 4870HQ boosts to 3.70GHz, while the 4980HQ boosts to 4.00GHz. The GPU also boosts slightly higher on the 4980HQ, but probably not so much that you'll notice.

So, in the end, the 2.8GHz model is going to be a good buy, especially if you want the fastest max single core speed. I think either CPU is going to throttle down under constant load as the cooling system reaches its limits. I suspect the 4980HQ will still run at a higher overall speed because it's a better bin and should be more capable of maintaining higher clocks. You won't see the boost speed from either for a sustained amount of time.

Great info. Mine probably won't have a dGPU, as organicCPU pointed out above. So if the temps are likely to be the same, I'd probably go for the 2.8GHz.

By the time of writing my 2015 15" MBP 2.8 GHz is for 1 year and 3 month almost 24h/7d in use without noteworthy problems. If rendering images (Blender in my case), the fans are running loud all the time, but temperature seems to be o.k.. I didn't notice significant throttling, though never kept an eye on this. How would you measure or track this?

Also great info, to hear it's running reliably like that.

I'd probably be using Blender as well at some stage (along with Rhino, SolidWorks, Sketchup, maybe ZBrush, Vray, etc). You're right - the MBP models I'm looking at have no dGPU. I'm under the impression this is actually better, if I want to add an eGPU at some point. Combining good MBP portability with desktop-like rendering performance.

I didn't know I'd be missing features from programs like Photoshop without dGPU though. Started another thread about that here.

To me, the Radeon dGPU's were never a benefit that I could see, since all my photo rendering software only works with Nvidia dGPUs with CUDA anyway. So thought I could save some weight and battery life having no dGPU.

 

[Darmok N Jalad]

Great info. Mine probably won't have a dGPU, as organicCPU pointed out above. So if the temps are likely to be the same, I'd probably go for the 2.8GHz.



Also great info, to hear it's running reliably like that.

I'd probably be using Blender as well at some stage (along with Rhino, SolidWorks, Sketchup, maybe ZBrush, Vray, etc). You're right - the MBP models I'm looking at have no dGPU. I'm under the impression this is actually better, if I want to add an eGPU at some point. Combining good MBP portability with desktop-like rendering performance.

I didn't know I'd be missing features from programs like Photoshop without dGPU though. I'll start another thread about that.

To me, the Radeon dGPU's were never a benefit that I could see, since all my photo rendering software only works with Nvidia dGPUs with CUDA anyway. So thought I could save some weight and battery life having no dGPU.

Photoshop does use the Iris Pro 5200 GPU, though a dedicated GPU would certainly be more powerful since it's not sharing resources with the CPU.
https://helpx.adobe.com/photoshop/kb/photoshop-cc-gpu-card-faq.html

 

[Hoff]

Photoshop does use the Iris Pro 5200 GPU, though a dedicated GPU would certainly be more powerful since it's not sharing resources with the CPU.

Excellent point. Makes sense, but never really thought about how the intel graphics are sharing resources with the CPU. Possibly another good reason getting the 2.8 instead of the 2.5Ghz.

Thanks for link to the Photoshop GPU FAQ. Definitely want some of those GPU only features.

Would a dGPU get in the way of adding an eGPU later?

 

[organicCPU]

To me, the Radeon dGPU's were never a benefit that I could see, since all my photo rendering software only works with Nvidia dGPUs with CUDA anyway. So thought I could save some weight and battery life having no dGPU.

Affinity Photo and Affinity Designer are utilising the Radeon dGPU as well as Adobe CS6 apps. If there are problems with some certain buggy app, that absolutely can occur, I use gfxCardStatus to switch manually to integrated Iris Pro.
I had preferred a Nvidia CUDA option as well, but that wasn't offered. The NVIDIA GeForce GT 650M in a 6 years old 2012 15" MBP is still working perfectly 24/7. I have no experience with eGPU so far.

Try the Intel Power Gadget.

Thank you for that hint. I'll report back about CPU throttling while rendering with Blender.

 

[Darmok N Jalad]

From what I gather, Photoshop and Lightroom will only use the GPU that is driving the display. I don't know how that would work with an eGPU. I don't know how it works with Photoshop, but as a Lightroom user, I can say that, at leasing in that program, some folks claim to have better results by disabling the GPU acceleration. I've used it both ways, and it's not like either option is unusable, or that one feels revolutionarily better than the other.

 

[Wags]

Have the dGPU ones been on refurbished store ?

 

[Bravo3013]

Excellent point. Makes sense, but never really thought about how the intel graphics are sharing resources with the CPU. Possibly another good reason getting the 2.8 instead of the 2.5Ghz.

Thanks for link to the Photoshop GPU FAQ. Definitely want some of those GPU only features.

Would a dGPU get in the way of adding an eGPU later?

A dGPU would not get in the way of adding an eGPU later. It is however much easier to setup an eGPU on machine without dGPU than one with. The 15" mid 2015 without dGPU is a perfect machine for setting up an eGPU at the moment. Be aware that Apple might not provide native eGPU for TB1/TB2 users in the coming updates.

 

[Hoff]

Be aware that Apple might not provide native eGPU for TB1/TB2 users in the coming updates.

If Apple wants to play that game I will be very disappointed.

So then, how to keep only the old OS that does support it? Or downgrade OS if needed?

 

[Bravo3013]

If Apple wants to play that game I will be very disappointed.

So then, how to keep only the old OS that does support it? Or downgrade OS if needed?

Yes I will be disappointed too as I have TB1 mac. Personally I stay on macOS 10.12.6 to ensure compatibility. It might also be the case that there will be support for TB1/TB2, we just dont know yet. It is noteworthy that the latest 10.13 beta just broke support for TB1/TB2 eGPU, but that might be a glitch.

 

[Hoff]

It is noteworthy that the latest 10.13 beta just broke support for TB1/TB2 eGPU, but that might be a glitch.

Hope so.

Speaking of glitch, I JUST read that you can't bootcamp Windows 7 on this 2015 MBP. Is that true? That was my plan, so this might be a deal-breaker for me

Does anyone know the details about this?

(I have legacy software running best on Win7)

 

[kudos212]

adding an egpu without

It is however much easier to setup an eGPU on machine without dGPU than one with.

It really isn't that hard. I wouldn't hold off on the dgpu just because at a "later point" you plan on adding an external one. You will also have to use an external monitor when you get one to fully take advantage of it. If I were you I would find a maxed out 2015 MacBook Pro used somewhere as it's already a 3 year old computer and using just the integrated graphics wouldn't be worth it.

 

[organicCPU]

No CPU throttling noticed while rendering for about 1 hour with an average CPU speed of 3 GHz (4 cores). Fans were loud, CPU hot, but I guess not too hot. Blender utilises AMD dGPU.

 

[Hoff]

adding an egpu without

It really isn't that hard. I wouldn't hold off on the dgpu just because at a "later point" you plan on adding an external one. You will also have to use an external monitor when you get one to fully take advantage of it. If I were you I would find a maxed out 2015 MacBook Pro used somewhere as it's already a 3 year old computer and using just the integrated graphics wouldn't be worth it.

Ok, thanks for insights.
I may still not get a dGPU. Sounds like it may lead to more problems than benefits.

https://forums.macrumors.com/thread...periencing-problems-related-to-video.1973382/
[doublepost=1519968453][/doublepost]

No CPU throttling noticed while rendering for about 1 hour with an average CPU speed of 3 GHz (4 cores). Fans were loud, CPU hot, but I guess not too hot. Blender utilises AMD dGPU.

Great info, and cool looking render.

Looks like you're pretty close to 100 deg. C. But that's great if there's no throttling. Also interesting that Blender now works with AMD GPU.

 

[Bravo3013]

I have do not have any hands-on experience of the 2015MBP (Considering buying one actually, without dGPU), but I do know that the mac will throttle during a longer period of high load, either due to thermal or power limitations.
@organicCPU that is actually some very good results! But be aware that the lifetime of the chip is drastically reduced if it reaches 100°C often or for longer periods.

If you want a longer lifespan of a MacBook Pro an eGPU is really recommended, as the Machine would run cooler. You would also get a lot better graphic performance. But eGPU is expensive to some degree, depends on how you look at it.

@kudos212 It is not a problem to setup an eGPU on a machine with dGPU, but it is easier to setup on a machine without dGPU, as there isn't any conflicts between them. I would disagree with your statement saying the mid2015 15" without dGPU isn't worth it. The machine is in fact quite good, still has great processing power and a lot of ports and very easy to setup eGPU on. The price for the machine on the other can be discussed. Apple is charging a lot for nearly 3-year old machine, but that doesn't mean it is not worth it for some users. Again, it all depends on your needs.

Hope so.

Speaking of glitch, I JUST read that you can't bootcamp Windows 7 on this 2015 MBP. Is that true? That was my plan, so this might be a deal-breaker for me

Does anyone know the details about this?

(I have legacy software running best on Win7)

I just checked BootCamp support page, and it says that mid-2015 is not fully compatible with Windows 7. You can install Win8.1 or 10 in BootCamp. I do believe that you can force BootCamp to install on the mid2015, but some drivers and keystrokes (like screen-brightness) might not work as expected.

 

[organicCPU]

Looks like you're pretty close to 100 deg. C. But that's great if there's no throttling. Also interesting that Blender now works with AMD GPU.

Yeah, there were peaks at 100°C, but average temperature was around 96°C. AFAIK AMD support was recently added in Blender 2.79. It seems that the upcoming 2.80 release can even utilise OpenCL without dGPU (see screenshot).

But be aware that the lifetime of the chip is drastically reduced if it reaches 100°C often or for longer periods.
If you want a longer lifespan of a MacBook Pro an eGPU is really recommended, as the Machine would run cooler. You would also get a lot better graphic performance. But eGPU is expensive to some degree, depends on how you look at it.

Thank you for pointing on that. By now, I've been mainly used the CPU for rendering. I'll check out, if I could benefit from dGPU rendering aside from previews or viewport imaging. If dGPU rendering turns out to be reliable, I'll take a closer look at eGPU.
Concerning the temperature, it seems to be possible to limit the CPU with apps like Instruments, cputhrottle, App Tamer or AppPolice to lower the temperature. Though I've heard of problems at soldering joints of older iMac graphics cards while playing too much demanding games, I was expecting that meanwhile the native power management would be good enough to prevent damages caused by high temperatures. What maximum CPU or GPU temperature do you recommend for longer or continuous operation without harming the MBP?

 

[Bravo3013]

Yeah, there were peaks at 100°C, but average temperature was around 96°C. AFAIK AMD support was recently added in Blender 2.79. It seems that the upcoming 2.80 release can even utilise OpenCL without dGPU (see screenshot).

View attachment 753047


Thank you for pointing on that. By now, I've been mainly used the CPU for rendering. I'll check out, if I could benefit from dGPU rendering aside from previews or viewport imaging. If dGPU rendering turns out to be reliable, I'll take a closer look at eGPU.
Concerning the temperature, it seems to be possible to limit the CPU with apps like Instruments, cputhrottle, App Tamer or AppPolice to lower the temperature. Though I've heard of problems at soldering joints of older iMac graphics cards while playing too much demanding games, I was expecting that meanwhile the native power management would be good enough to prevent damages caused by high temperatures. What maximum CPU or GPU temperature do you recommend for longer or continuous operation without harming the MBP?

Hmm it is actually not easy to recommend a certain temperature, as the chips are designed to be able to reach 100°C (at least for shorter periods). I believe the CPU are more comfortable at higher temperatures than GPUs. The reason is that the CPU tends to be more durable than dGPUs (At least in the past/my experience). I would believe you are fine by running the machine at 100°C as long as you only do it for shorter periods and not frequently. You can run the machine at 100°C for longer periods as well if you really need to, but that may reduce it's lifespan. I can not say that your machine will have reduced lifespan, but the percentage of a shorter lifespan is much higher.

It is recommended to have the machine as cool as possible at all times. I would belive (Can not state this with 100% accuracy) that the optimal temperature under load on MBP is in the 70-80°C zone. Although this might be hard to achieve with higher workloads. Do also remember that your work shouldn't suffer from concern over thermal issues. If you need to run the machine at high workloads, you should do it, just beware that the lifespan statistically decreases. The mac is created for high performance, so you should not limit your usage if you need/want it!

Another thing i really recommend is that you/everyone install the program called Macs Fan Control. It lets you setup a more aggressive fan "policy". It lets you be in charge of the fan settings. With this program you can for example set the fans to kick in if the CPU temperature rises above 50°C. With the default apple settings the fans dont really kick in before the CPU hits about 75°C. If you program the Mac to start the fans at lets say 50°C, it would delay the effects of thermal throttling as the fans start earlier and you get a cooler machine. It will make the mac more noisy, but might be a worthy tradeoff for longer lifespan. You can also disable the program for certain times if you rather want a more silent machine from time to time.

 

[Hoff]

From what I've read, I would feel much more comfortable if the temps were down around 90 deg. C or lower during rendering. I would suggest a cooling pad - either with fans, or I've read about some "fanless" cooling pads. They seem to lower temps by about 10 deg C. If/when I get a mac, I'll likely be using one.

I read of a guy who fried his 2015 MBP during rendering, although sounds like he'd been rendering on it over a number of years. And he lives where it's about 30+ deg C all year round. So it can happen.

Main takeaway - I highly recommend a cooling pad for rendering.

 

[Queen6]

From what I've read, I would feel much more comfortable if the temps were down around 90 deg. C or lower during rendering. I would suggest a cooling pad - either with fans, or I've read about some "fanless" cooling pads. They seem to lower temps by about 10 deg C. If/when I get a mac, I'll likely be using one.

I read of a guy who fried his 2015 MBP during rendering, although sounds like he'd been rendering on it over a number of years. And he lives where it's about 30+ deg C all year round. So it can happen.

Main takeaway - I highly recommend a cooling pad for rendering.

Very much a "canned" response from the days when the 15" MBP ran extremely hot, equally some points may be of use to you:

Being an owner & user of the 15" MacBook Pro since forever; Over the years the 15" has frequently struggled with it`s thermals, especially when an external display is connected as the dGPU engages by default, internal temperatures soar, equally there are some steps that can be taken to reduce the systems temperature;

• Elevate the rear, aluminium passive coolers generally work best (I use RainDesign`s mStand & iLap), even small portable risers such as ORICO's Creative Laptop Stand can make a difference, very handy for those on the "go".
• Increase base fan RPM to 3K or as much as you are comfortable with (MacsFanControl or SMC Fan Control)
• Limit the dGPU`s usage with gfxCardStatus
• Swap out Chrome for Chrome Canary as it can be more optimised for OS X and may extend battery run time, reduce thermals etc.
• Swap out VLC for Movist as again it`s a reduced load on CPU/GPU
• Uninstall or block Flash
• Install an ad blocker Wipr or AdGuard works well
• Powered coolers are very much a "mixed bag" when it comes to Mac portables, you need one that has a high capacity (100 CFM minimum) and preferably a large single fan, this can help to keep the 15" internal fans below 4K which for many is good enough as often it`s this point and beyond where the fans become intrusive and annoying. Don't expect a powered cooler impact internal temperatures, beyond a couple of degrees
• Older notebooks can benefit from cleaning of the cooling system
• Retina`s can benefit from cleaning of the cooling system, as the heat syncs are far smaller and loose efficiency faster, due to build up of dust/debris etc.
• Replacing the thermal paste has been hit & miss, some with very positive results, some with no improvement over stock. Personally I would only do this on a Mac Portable that was either very old, or one that I can confirm was definitely running a lot hotter than stock.
• If your MBP has a discrete GPU, it will fire up when an external display is connected as default, temperatures will rise rapidly.
• Consider a specific vertical stand when using a MPB in "Clamshell" mode allowing for greater circulation of air. Some recommend inverting the MBP in the stand with the exhaust at the top & intake at the bottom (Retina)
• Another option for static setups is a USB powered fan strategically placed so it blows across the MBP keyboard deck (air flow L-R above & below the keyboard)

The key to a quiet life with a 15" MacBook Pro is several incremental changes that can and do add up to reduce thermals. From my experience over the years if your going to push a 15" hard the fans are going to max out fast, with associated temperature & noise. If your using it with a moderate load, life can be made quieter. For the most part your MBP runs hot as that`s how Apple designed it, this is the trade off for thin & light...

Like it or loath it, there's good reason why the majority of Windows MBP counterparts have significantly more cooling & vents, nor is it due to their design teams being inept. Apple simply places form over function first in many circumstance.

The 2015 15" MBP has more aggressive fan curve than the older models, likely to stave off another round of mass dGPU failure. There is no way to disengage the dGPU when an external monitor is connected, all one can do is take small steps to reduce the overall temperature to a level where the fans will not spool up to an unacceptable level, generally 4K+ RPM.

The old adage still applies; it`s easier to keep a system cool, than cool-down an already overly hot machine. This being said it`s not strictly necessary, equally it`s nice to know that there are some options for reducing temperature out there, and a quieter life.

As for the 2.8GHz CPU answers to that question undoubtedly lie here:

https://forums.macrumors.com/thread...al-throttling-and-overheating-github.1731178/


Q-6

 

[turbineseaplane]

Swap out Chrome for Chrome Canary as it`s generally more optimised for OS X and will extend battery run time, reduce thermals

This true? I didn't know this.
Great tip!

 

[Bravo3013]

Very much a "canned" response from the days when the 15" MBP ran extremely hot, equally some points may be of use to you:

Being an owner & user of the 15" MacBook Pro since forever; Over the years the 15" has frequently struggled with it`s thermals, especially when an external display is connected as the dGPU engages by default, internal temperatures soar, equally there are some steps that can be taken to reduce the systems temperature;

• Elevate the rear, aluminium passive coolers generally work best (I use RainDesign`s mStand & iLap), even small portable risers such as ORICO's Creative Laptop Stand can make a difference, very handy for those on the "go".
• Increase base fan RPM to 3K or as much as you are comfortable with (MacsFanControl or SMC Fan Control)
• Limit the dGPU`s usage with gfxCardStatus
• Swap out Chrome for Chrome Canary as it`s generally more optimised for OS X and will extend battery run time, reduce thermals
• Swap out VLC for Movist as again it`s a reduced load on CPU/GPU
• Uninstall or block Flash
• Install an ad blocker Wipr or AdGuard works well
• Powered coolers are very much a "mixed bag" when it comes to Mac portables, you need one that has a high capacity (100 CFM minimum) and preferably a large single fan, this can help to keep the 15" internal fans below 4K which for many is good enough as often it`s this point and beyond where the fans become intrusive and annoying. Don't expect a powered cooler impact internal temperatures, beyond a couple of degrees
• Older notebooks can benefit from cleaning of the cooling system
• Retina`s can benefit from cleaning of the cooling system, as the heat syncs are far smaller and loose efficiency faster, due to build up of dust/debris etc.
• Replacing the thermal paste has been hit & miss, some with very positive results, some with no improvement over stock. Personally I would only do this on a Mac Portable that was either very old, or one that I can confirm was definitely running a lot hotter than stock.
• If your MBP has a discrete GPU, it will fire up when an external display is connected as default, temperatures will rise rapidly.
• Consider a specific vertical stand when using a MPB in "Clamshell" mode allowing for greater circulation of air. Some recommend inverting the MBP in the stand with the exhaust at the top & intake at the bottom (Retina)
• Another option for static setups is a USB powered fan strategically placed so it blows across the MBP keyboard deck (air flow L-R above & below the keyboard)

The key to a quiet life with a 15" MacBook Pro is several incremental changes that can and do add up to reduce thermals. From my experience over the years if your going to push a 15" hard the fans are going to max out fast, with associated temperature & noise. If your using it with a moderate load, life can be made quieter. For the most part your MBP runs hot as that`s how Apple designed it, this is the trade off for thin & light...

Like it or loath it, there's good reason why the majority of Windows MBP counterparts have significantly more cooling & vents, nor is it due to their design teams being inept. Apple simply places form over function first in many circumstance.

The 2015 15" MBP has more aggressive fan curve than the older models, likely to stave off another round of mass dGPU failure. There is no way to disengage the dGPU when an external monitor is connected, all one can do is take small steps to reduce the overall temperature to a level where the fans will not spool up to an unacceptable level, generally 4K+ RPM.

The old adage still applies; it`s easier to keep a system cool, than cool-down an already overly hot machine. This being said it`s not strictly necessary, equally it`s nice to know that there are some options for reducing temperature out there, and a quieter life.

As for the 2.8GHz CPU answers to that question undoubtedly lie here:

https://forums.macrumors.com/thread...al-throttling-and-overheating-github.1731178/


Q-6

How will swapping out Chrome Canary for Chrome be a good move in the long term? Chrome Canary is basically the newest experimental version of chrome if I remember correctly. It will have new features, but will crash a lot. Why would it be more optimised for OS X compared to stable releases of Chrome?

 

[Queen6]

How will swapping out Chrome Canary for Chrome be a good move in the long term? Chrome Canary is basically the newest experimental version of chrome if I remember correctly. It will have new features, but will crash a lot. Why would it be more optimised for OS X compared to stable releases of Chrome?

Chrome if I remember correctly several levels of development with Canary being one of them. Canary has always been stable for me and it did have lesser impact. This list is formulated over many year's of dealing with overly hot MBP's something's will work better, some won't. Simple solution is to try and observe if there's any positive impact. One thing is certain no single change makes these older MBP's run much cooler

Q-6
[doublepost=1520221200][/doublepost]

This true? I didn't know this.
Great tip!

Something you have to try and see I always had good results with Canary, nor did I find it unstable. Beauty of Canary is that it happily resides with regular Chrome, nor does it interfere, unlike the Beta and Dev Chrome channels.

End of the day you just need to try as Canary is in perpetual development. It's about feature and performance, it worked for me so I keep it in the list.

Q-6