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 890GTX-G65.
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.
hd5770 is very good card but i'm not sure if you can run PhysX on 2x5770 may want to check with ATI/Nvidia/mobo experts on this forum,as for cooling your cards (5770 are one of the coolest running card out there .I would suggest reapplying new TIM like MX-2 and improving you case air flow