I have a simular setup as seen below in my post, and vista 64 weither gaming, or not its still just really nice. Tried windows xp 32 and had to swtich back to vista 64bit which really takes advatage of the cpu, and ram. Not to mention I can even run games that came out before 64 bit os so I am yet to find a game I cant play on vista 64.
Its become really stable and xp is losing support soon. And dx10 is really nice to play expesically running a card(gpu) like you'll have.
Phenom 9850 x4, Asus MVP Deluxe , 8gigs OCZ ddr2 1066, Visiontek 3870x2, Xfi Elite,2x WD Raptors 10k in raid 0,Antec 1000watt, and Cooler-master Stacker 830 Evolution.