I've gone ingame to double check my settings and can confirm I played it at named settings smoothly:
6800gs, 3.2ghz c2d, 2gb.
I did find though, that the smoke from inpacting bullets kill fps making fps around 25-30 for me instead of the usual 40 outside or 80 inside buildings. Try to find a tweak to reduce or disable the smoke from bullet impacts, should boost your fps a lot when shooting.
It was only noticable for me though with a lot of bullet impacts up close ( ie. shooting a wall 1 inch away front you ) and that impacts far away didn't really affect performance.