Did some casual testing and found some interesting / upsetting stuff.
I have a Q6600 clocked to 3g and im' using vista x64
i run my game at 1680x1050, all very high except post-processing.
i made a custom autoexec.cfg as well to allow very high / high
when running a certain battle sequence(no spoilers) my quad got an average of 14-17fps (this is when you are being given your mission in the first big battle). when the program ran with only 1 core enabled, that core was constantly at 100% and ran almost identically to my normal game which supposedly was made with multi core in mind. i lost 1 frame. now it averages 13-16 fps.
using just two cores, performance was the same as single core (maybe .5 frame better). neither of the cores were maxed out, and kept fluctuating between 40-60%
i tested it again with all cores enabled and for most of the time, only once core got maxed out, and the second one would just kind of twitch every once in a while.
this leads me to believe that we will be most probably be getting a patch or two on launch day. in my opinion, this code was rushed to get gold and meet the release date, but i have faith in crytek .... busting their asses so that when the majority of people get this game, they won't be AS disappointed with the performance. good game so far. my pre-order hasn't come in yet (gets in wed) but i just wanted to test what was available to me NOW.
also of interest ...... the BIGGEST stealer of fps is the cvar that enables object motion blur. that shaved 11 fps off of my pety 24 fps.