I have to agree with red here.
My spec, Intel Quad core Q8200, 4GB RAM, 256GB SSD, Radeon HD4670
Running Crysis, I'm having to use medium settings, with 1024x768 (I think its 768) resolution, and in fairness it's lagging out and dropping below 20FPS when all hell breaks loose. In the beginning it handles it well, but as you progress and enemies appear more, and you have more going on, the GPU is struggling to keep up and was even crashing in later levels.
You need a much better card than the one you currently use unfortunately.