The best test is to compare at lower resolutions. If I remember right, the lowest rez will show the cpu limitation as your cards really don't stretch their legs until the higher resolutions.
You would probably see the 460 begin to overtake the 8800s at 1680x1050 or so, using AA and higher settings...I think that's right
Let me google for a sec..
EDIT: Can't find a direct comparison using your cards - but if you get the same fps at lower rez that you do at higher, then it's probably your cpu.