iMac i5/i7 heat/noise?

[Kutuzov]

When reading on this forum I came across the question if i7 runs hotter/becomes noisier than i5 with normal usage. There were two different ideas about this. They were significantly different so I thought maybe someone who knows about this stuff can give a definite answer as to who is right? Below are quotes from that thread,
https://forums.macrumors.com/threads/1484066/

Disabling hyperthreading will not cut temperature.

Unless you are working the machine flat out (in which case, the i7 will complete jobs quite a bit faster), it will run cooler than an i5 due to getting the work done quicker and returning to idle quicker - thus being able to turn parts of itself off and/or reduce clock speed more often. Disabling hyperthreading will simply cripple the CPU and make it run higher clock speeds (thus generating more heat) for longer, and getting your jobs done slower.

The i7 already has pretty advanced power/thermal management inside it so the CPU itself can decide when is appropriate to turn bits of the CPU off, down-clock, etc.

Most people don't need an i7, but worrying about heat and using that as a reason to go for an i5 is just nonsense.


If you encode/transcode video, the hyperthreading on the i7 will enable it to get jobs done much faster.

I appreciate you chiming in, thanks! However, after researching this topic around the net, it seems to be a clear perception by people using i7 for overclocking, that hyperthreading will make the CPU run hotter (more parts in the CPU constantly running), often resulting in 10C higher temps. For that reason the i7 is reportedly harder to overclock, and some actually turn off HT to get higher core speeds for gaming. I'm not saying I'm an expert or anything, just reporting what I've read various places.
I am worried about this new thinner design, and the hot running Ivy Bridge (esp. i7) CPUs and a high-end graphics card. I'd rather buy the i7, but if i5 will give less noisy computer when gaming and similar (lower temps = fans have to work less), then I'd go for i5.
I guess the smart thing is to sit on the fence for a few extra weeks, and see how the new iMac turns out.

 

[throAU]

The long and short of it is this:

Yes, an i7 CAN run hotter if you are running it full speed.

However, it doesn't need to run full speed for as long, to get the same work done as an i5.

I doubt it will be noisier - the max fan speed is still 6200rpm (? is on the MBP anyhow) on both machines.

To get a long cpu intensive job done, the i5 will run the fans for longer as it will take longer for the job to complete.

 

[Mac32]

I tried to ask about this, but the problem is you can't overclock or disable hyperthreading on i7 iMacs, so you would need several iMac models to test this. Therefore you'll most likely get assumptions here, and not real objective/factual answers.
If you look at overclockers' forums, you'll find that the hyperthreading in i7 typically add about 10 degrees at full load (sometimes more, sometimes less). However, these are overclocked CPUs, so the the added hyperthreading heat would be exaggerated.
Anyway, the i7 CPUs have to get hotter because they draw more watts at max load than i5, but how much difference in the thin, closed iMac design, who knows..

My biggest concern is gaming, as the 680mx card is also bound to get hot. I guess we'll find out eventually when the 27'' iMacs start to ship. I too prefer a more quiet cool-running machine, if possible.