My wife, who is decidedly fantastic, knew I'd wanted to mess with crossfire and bought me a second Sapphire 5870 for my birthday. I knew my old 650W PS wouldn't do it, so I upgraded to the 850 above.
I gladly threw in the Sapphire and tried out crossfire. Much to my dismay, I noticed a lot of new artifacts in the BF3 beta, and black lining in BF:BC2. Using MSI Afterburner I tracked down temps and found when crossfire is enabled......
My temps at idle are ~55(secondary)/~70(primary). At load ~80/~93 (that's 93C with 100% fan). And the only reason it stays at 93 is b/c the card throttles down from 850 to 600. By the way, these temps are with the side of my case removed.
I've got both cards in the Sabertooth's x16/x16 configuration and, as I'm sure you know, they're right on top of one another. I do have a 3rd PCI-E slot that's more distant (i.e. has better airflow), but it's only at 4x.
Question 1: How the holy heck can I get this heat under control?
Question 2: I heard 16x/4x performance hits aren't necessarily that bad. Will I see dramatic underperformance at that level?
I don't want to sell the cards, or buy another, so please help me work with what I have. Having recently spent a bunch of money on this, I'm loathe to "just buy a better single GPU." I'd also like to avoid expensive aftermarket coolers, especially since I understand they block SLI.
It is normal that the top card heats up much more than the one below due to restricted airflow, moving it to the x4 slot would make about 10% difference on a 5870 performance - wise .
But the problem here is the case you're using, it has very little ventilation options and it doesn't make a good match with lots of hot-running power hungry equipment you're using, even if you let the side of the case open it still won't make a good airflow, having a couple high CFM 120mm fans blowing directly towards the cards will make a difference, I suggest you upgrade your case to something like this: http://www.amazon.com/Cooler-Master-Tower-Case-RC-912-K... and fill in the optional fans