I find it kind of interesting how people are getting such widely differing results with similar systems. Game seems to be much more RAM/GPU dependent than CPU, as my quad never goes above about 40% per core during play, nor do i ever get any lag whatsoever system wise.
I can max everything without any noticeable decrease in FPS.
Rig:
Modified HP M8530f
AMD Phenom X4 2.2ghz
7 gigs dual channel ram
Radeon 4890 OC PCS+
700w StealthXstream psu.
I can also max Crysis Warhead and Empire Total War without issue. Never tried the original Crysis.
