These are benchmarks running the exact same system as you but with two GTX's in sli.mrcheese said:40 FPS in everything but the most hectic gunfights and 25-30 FPS during the boss battle (this was a noticeable drop, but with a noticeable reason).
I'm NOT running it on DX10, i'm using cvar tweaks to enable very high graphics on DX9 which may be where the performance boost is coming in, I don't have vista hogging up a load more resources.
And I assure you, every setting was as high as I could get it except antialiasing, where i settled for 8XQFSAA.
At the other end of the spectrum, my housemate's pc is woefully dated and he can run it at 30FPS average on custom graphics settings with most in the medium range. I think he's running an athlon XP 2600, radeon x100 pro with 1 ig of RAM and he's running it well enough to enjoy it. So yes, i'd say a £300 / $600 pc would run it pretty well.
WinXP service pack 2, Dx9 Very high all settings. 1600x1200 8XQFSAA. Driver revision 169.13(best for crysis)
the tests are located in the bin32 folder of crysisGPU TEST
Average FPS: 21.18
Min FPS: 9.93
Max FPS: 25.57
CPU TEST
Average FPS: 19.76
Min FPS: 7.88
Max FPS: 26.54
You might not be running an fps counter and 40fps is just a generous assumption; because I can say with great confidence your not getting it. I'm not just basing this on my results, but every result posted on the incrysis.com forums. 8xAA is complete overkill for that resolution and I assume an average size monitor, I'm not sure I believe your running it.