PC crashes after installing another HD 5850

[sprawl]

I recently got another HD 5850(old one is a Sapphire reference card, new one is a cheap XFX with an egg cooler), and my PC started crashing. I'm using a Corsair TX850W, a Phenom II X6 1100t, 8GB Corsair Dominator ram on an ASUS Crosshair IV Formula. I tried underclocking the cards, and it remained stable for longer, but ultimately it would still crash in FurMark. Temps seem good at around 70C load.
I'm now reinstalling Windows 7 x64 + all drivers, hoping that it might be a software problem. The PC is stable in Prime95, and in FurMark with only one graphics card.
Anyone has any idea what might be the problem? Is the XFX card faulty?

 

[sprawl]

So I think I found the problem, after reinstalling Windows 7, and only the GFX drivers, the PC still crashes.
I tried using only the XFX card in the PCI-E port I used for my old card - it crashes in under 2 minutes in FurMark(below 60C). Tried switching to the old Sapphire card, no crashes! RMA'ing the card(for the second time), and getting a Sapphire HD 5850 Vapor-X instead. I'm done with cheap cards with egg coolers!