Yeah my card stutters with Crysis (Obviously) and also a tad with mirrors egde.
I'd say it's the GPU, I used to have a 9600GT, and can safely say this 4850 I have now is quite a bit better
I can max out GRID @ 1920 X 1200 8AA 16AF, I know I wouldn't be able to do that with my old GT. Back then I was playing at 1440 x 900 16AA 16AF Max Settings IIRC