Yeah, can you check if both your GPU and CPU clock up when you game? If you have 2 screens, just put the GPU-Z's sensor tab and the main tab of CPU-Z on the other screen and run a game. I also think there's a way to have an OSD in games when running RivaTuner that will show you all the clocks too.
If that one doesn't work, no idea. It doesn't make much sense then

Also, did you install DirectX9 ? It doesn't come standard with Vista/Win7, you have to manually download it from Microsoft and install it. It could explain the low scores in Crysis (Enthusiast = Crysis Warhead = DX9). Also, All Enthusiast and AAx4 = no way, no matter the power you're throwing at Crysis. Well, maybe HD5870x2 QuadFire...