Pre-Post Edit: I realized asking 6950 specific speeds/temps is probably excessively specific, so I'm looking for this advice in general too.
I have a dual 6950 setup that I use for gaming, bitcoin mining, and GPU cracking. The first one isn't too much of a worry for me, as what I play really doesn't stress my cards too badly at the resolution my monitor can do, but the other two have the ability to run my cards at essentially 100% utilization constantly. Right now there are no overclocks applied (not even Overdrive) and they haven't been flashed to 6970's, though I'm sure that will come later.
I can keep my system temperature around 30*C, and would like to know for the 6950's, what is the recommended trade-off between fan speed and operating temperature for maximum component life at stock speeds? Currently I find my cards run 66 and 67 celsius at 42% and 49% fan speed.
I've read online that if you're seeing temps at/below 62 you should drop fan speed but don't want your cards above 80 or ideally 70, but wanted to get a broader base of opinion/expertise.
That kind of advice would to me be specifically aimed at trading noise for heat. If your cards are not making excessive noise then it would be madness to turn the fan down. The cards these days come with some pretty decent warranties as long as you are prepared to pay that little bit extra for the quality products that these warranties come with. Running the fans lower than factory defaults in an attempt to increase the life of the card seems a little fanciful to me.
Without using Afterburner my fans sit at about 32-35% until GPU temps hit 80*C where they sit at 35%. The cards slowly climb to 82 and 84 degrees with fan speeds at 35 and 37 precent respectively. They're quiet sure but too hot for me to be comfortable leaving them at constantly.
Well personally i look at 75 as the top end. I read that cards these days are tested up to and slightly above 100 but i don't personally fancy getting anywhere near that.
I would think that either over clocking the cards or turning them into 6970's would mean you have little choice but to allow the temps to run up to about 80.
Its a little difficult without knowing the specific card (2-3% increase alters the temps a lot on my card, but as a ball park i would aim for a curve that gives you around 75 and as long as the fan speed is not causing excessive noise it should be ok
Specifically in reply to your question i would want the temps down in preference to the fan speed being lower.
You can put a new cooler on but replacing the memory chips is a bit more difficult.
I found out there is a thread on the bitcoin forums that somewhat addresses this too. Opinions there seem to be fairly broad on the spectrum - some think 75 is a little warm, some think up to 85 is ok, others are more worried about fan life than temp.
Worth noting that in tuning your rig for most of these math-related gpu apps you can turn down the memory speeds and voltages to reduce heat and draw without hurting your application's performance since it doesn't get used much, which should help fan speed too.
Seems like I should be in the fairly safe range with my current numbers, but I'd still welcome anyone else w/ input to post.