I picked up 2 XFX 5770's and they run great, much better than my GTX 460.
Just sad that the FPS dips a lot in games that allow dedicated Physx. (BC2 goes down to 5 fps when a building gets hit with destruction 2.0)
I haven't started overclocking the cards yet. The bottom card is doing great, hasn't broken 55c. The top card however, just hit 85c. I usually like to keep my hardware at 70c tops, so I'm looking to buy a new cooler for it. I will be purchasing off of Newegg, but I don't see much for compatibility.
Motherboard is MSI
PSU is Rocketfish Gaming 500 Watt.
Case is NZXT Phantom; it has great airflow.
The cooler cannot take up more than 2 slots since my board has the pci-e 1 slot away from each other.
Currently looking at Zalman and Xigmatek coolers.
Not really sure how much another 200mm case fan would help but it's a lot cheaper than getting a cooler another thing you could do would be to take off the stock cooler and replace the TIM with arctic silver 5 that should cut about 3 or 4 degrees the fan another 5 If it is still running dangerously hot then get a cooler but first try the above methods they're cheaper and even if you end up do getting a cooler they will only improve things