Sapphire ME 7950 Crossfired in MP 5,1 advisable Yes/No?

[AlexMaximus]

Hi folks,

I have the machine in my sig. Right now, I use the machine for video editing and various Adobe programs.
Since I do use the Mac Pro for the occasional game on Windows 7 bootcamp at the moment I am ok with what I have. The existing Sapphire is not the best but not the worst to be in both IT worlds in only one machine. In a view months there are a number of games coming out that I can not skip for my life, such as the new Deus Ex and Fallout 4.
Now here ist the question for two possible scenarios I am looking at:

#1
Keep the existing Sapphire 7950 and add one more 7950 to use crossfire for the Windows game.
It would cost me arround 250 to 300 Euros for that. Pro: No driver hassle in OS X since I would have two Mac versions, less invest compared to #2, auxiliary 450 PSU would be needed. Con: less GPU power then #2

or

#2
Sell the existing Sapphire 7950 ME for 300 bucks and get a Nvidia 980 from MVC. Pro: Way better graphics all around. Con: Fiddly drivers, high shipping cost to Germany, higher cost, uncertain Nvidia Web driver situation, maybe more downtime for OS X ..

I am not sure which route to go. Somehow I would love to pimp that baby with a second white 7950 Mac Edition. It would be less money and more pimping with that Aux PSU (+ I really love mods) The Questions is this, how big would be the difference between Two 7950 Crossfired to One Nvidia 980 in Windows ??

What do you think, which scenario would you choose?

 

[Fl0r!an]

I'm pretty sure that Mac cards (especially HD 7xxx) have problems with Crossfire when used in Windows (read: bluescreen or something thus not usable at all). MVC might be able to confirm this...

 

[h9826790]

If you love mod, then you don't need an extra PSU, just go through the PSU mod (to get the power directly from the PSU), then you can install almost all GPU you want without any power issue (including dual AMD card in CF).

In term of gaming performance, I am quite sure a single 980 is better than 7950CF. Even though it may not be significantly better, but it should be better in term of the spec on paper, and also considering CF will have more driver issue than single card option.

If I were you, I may either go all the way to 980Ti (not 980) or 7950CF. The 980Ti just a little bit more expensive than the 980 (especially including the shipping cost), but IMO it's a much stronger card. And must stronger than 7950CF.

The 7950CF option is a better option for money. In fact, if I go this route, I will try to get a PC 7950 to do that to save more money. AFAIK, CF won't affected by the Mac EFI anyway (Update: just test this on my own rig, Mac EFI may affect CF. It's much better to boot from non-EFI BIOS for CF reliability). And any reference 7950 should able to pair up with the 7950 Mac Edition card (especially those with 2x6pin 800MHz non overclocked card).

But in either case, most likely I will go though the PSU mod, rather than install an extra PSU. (Update 1: It's my mistake, MVC's 980Ti can run with only 2x6pin internal power, so no PSU mod required)

However, at this moment, I personally will choose the 7950 route. It's just because I personally don't want to deal with those possible driver issue (especially I love to play around with betas / updated on my leisure time). But that's just me. If money is not a big issue, and driver is not the main concern. I will go for the 980Ti.

 

[h9826790]

I'm pretty sure that Mac cards (especially HD 7xxx) have problems with Crossfire when used in Windows (read: bluescreen or something thus not usable at all). MVC might be able to confirm this...

I've seen one case (on internet) was doing 7950 Mac Edition CF without any problem on a 4,1. However, I don't know if he boot the machine with the UEFI ROM or the Mac EFI ROM. And I don't know how's the stability. I just know he successfully did that (even with internal power only without PSU mod).

 

[MacVidCards]

Somewhere buried is a thread where I had a Cubix. Seem to recall that both 7950/70s having EFI was deal breaker. Gotta love that little switch.

 

[h9826790]

Just tested it. If any card use a Mac EFI ROM to boot, both card will have the ability to show boot screen. However, may have trouble to use crossfire.

So far, my tests result is as follow (Win 10, SSD via SATA 2 port in optical bay, no bootcamp driver installed, latest non beta CCC).

Both card boot from Mac ROM, stuck during boot (after crossfire activated).

Both card boot from non EFI ROM, takes a bit longer boot after crossfire activated. But can use it without problem.

The card attach to a monitor without EFI, but the other one boot from a EFI ROM. Boot screen still available from the non EFI card. Sometimes it can boot (I didn't time it, but feeling that cost more time to boot than both non EFI card), but sometimes it stuck. If boot successfully, crossfire will be available.

In any case, if crossfire no working properly. Recycle the crossfire option in CCC will fix it easily.

Update 1: Install bootcamp drivers won't affect the crossfire. And here is the 7950x2 Valley benchmark (everything maxed out with V-sync in 2560x1440).

 

[h9826790]

I only use mini 6pin -> 2x 6pin adaptor to run both card.

Both card only run at stock 800MHz, both card reduce to minimum stable voltage (0.887V and 0.912V accordingly) and limit to 130W TDP (+/-0%) in the BIOS to avoid overload the Mac Pro. (Under full load, the card will draw 30-40W from the slot, and 90-100W from the 6pin).

Under normal full load (Valley benchmark / games, NOT OCCT or Furmark), the card won't draw more than 95W from a single line. I know it's outside the 75W limit, but I am comfortable with it.

By running OCCT / Furmark, of course it may draw more than 100W, but never shut down the machine in any of my test. (Update 2: more tests show Furmark will draw 95W (stable) from the cable, and the rest from the slot. And never draw more than 100W in any test).

(Update 1: Problem fixed)
My only problem is that after my 7950 Mac Edition card RMA. Sapphire sent me a replacement that with a very poor cooler. The card overheat straight away. I open it up and replaced the dried out thermal paste. Helps a bit, but when I replace the paste. I realise there should be quite a big gap between the card and the GPU. I need to use a lot (around 3x normal) AS5 to make the cooler able to "contact" the GPU (I test it by applying the paste, put the heat sink back, and then remove it to check if the pea become a disc and cover the whole GPU). So now, the card works, won't overheat, but still very hot and very noise (60% fan and 88C max).

Is there any one know how to fix it? Any little mod on the cooler may work? Or use a copper plate to fit the gap?

Million thanks in advance.

 

[h9826790]

Problem fixed. I open the card. Cut these 4 screw hold bar a bit (half mm may be). And remove some extra thermal paste (I prefer to re-apply it, but I have no more paste on hand now). Now the card run Valley benchmark at 70C @ 36% fan speed with that poor reference cooler. Just very very little fan noise now. I am extremely happy with the result

 

[AlexMaximus]

Just tested it. If any card use a Mac EFI ROM to boot, both card will have the ability to show boot screen. However, may have trouble to use crossfire.

So far, my tests result is as follow (Win 10, SSD via SATA 2 port in optical bay, no bootcamp driver installed, latest non beta CCC).

Both card boot from Mac ROM, stuck during boot (after crossfire activated).

Both card boot from non EFI ROM, takes a bit longer boot after crossfire activated. But can use it without problem.

The card attach to a monitor without EFI, but the other one boot from a EFI ROM. Boot screen still available from the non EFI card. Sometimes it can boot (I didn't time it, but feeling that cost more time to boot than both non EFI card), but sometimes it stuck. If boot successfully, crossfire will be available.

In any case, if crossfire no working properly. Recycle the crossfire option in CCC will fix it easily.

Thank you so much!!!
Great reply, now I know. I guess I will stay with a one card design. The crossfire route is just to uncertain. Thanks again!