I recently upgraded my PC from a:
C2D e6600
4 gig 6400 DDr2
EVGA 8800 GTX
On win XP 32bit
to a:
Core I7 920 @ 3.2ghz
6 gig 1600 MHZ OCZ
2 x 4890 1 gig
on Win Vista 64 bit
I didnt see an improvement whatsoever with this game. Any other game (Including the dreaded Crysis runs perfectly). It hilarious how many Bohemia Fanboys cannot admit that this game is completely broken. After 10 Years of engine development Bohemia still cannot release an engine that runs good. The only consistent thing that i have noticed is really that the game is not optimized for multithreaded systems. Most of the people having performance problems have several core processors and multiple video cards. my 8800 GTX actually ran the game smoother than 2 4890's.
We can all hope that patch 1.03 improves performance and stability. However im not holding my breath. 10 Years of engine development has indicated otherwise.