I've been reading through a lot of fora regarding the 2GB vs 4GB issue in Crysis and these are a few impressions I have received(Plzz correct me if I am wrong ) :-
1. Anything over 2GB RAM will NOT help in framerates if one is using Win XP(32 or 64) or Win Vista 32 bit.
2. 4GB RAM in Vista 64 bit. Now, this is the controversial one. Many Vista 64 bit users report SLIGHT increase in framerates using 4GB RAM......but an equal number report NO increase in framerates !
3. What nearly all the Vista 64 bit users agree on is that having 4GB RAM, while not necessarily increasing framerates, almost definitely increase the SMOOTHNESS and loading times.
What this SMOOTHNESS actually means is that while the MAX FPS does not increase, the Minimum FPS DOES, especially in scenes involving heavy firefights....... a lot of textures are loaded into Memory and naturally, the more Memory you have more the textures can be stored in the faster RAM memory and so there is less(if any) usage of the slow swap file of the Hard Disk and so less stuttering in the Game.
In summary, Max FPS will depend upon the capabilities of your GPU...... the faster the better.
Min FPS using 4GB RAM will (or should) increase in heavily graphical-intensive situations, over 2GB.
Mind, I'm not saying that Min FPS will ALWAYS increase, but only in certain situations. So, simply doing Benchmarks may or may not show this increase in Minimum FPS....... but it certainly will improve the smoothness of the Gameplay, which is all that matters in this game I think.
Of course, 4GB RAM will make the System more future-proof.
Of course, all this is only for Vista 64bit.
Just my 2 cents