Security is the biggest benifit.
Able to use up to 128Gb of ram in vista ultimate.
Did I mention security. Kernal hardening helps prevent major nasties from recking havoc.
Stability. It is Damn stable.
With your hardware it would run like a dream.
Even though its considered by some a hinderance, driver signing! All drivers must be signed. For me that means better quality and more reliable drivers.
Was that 6?
In a word x64 rocks. Hope your installing Ultimate x64 on that cool system. I have it running here, and my hardware is close to yours but your got more RAM(2Gb here) a better CPU(C2D6550 here), our motherboards are about the same(intel Q35) and you got the better GPU(NV 7900 GT).
Yes, you sytem will ROCK!!!