[Fyron]

Rather negligibly in general. 5-10% performance gains are not worth $500-1000. Isn't the only real difference between the geforce 7xxx line and 8xxx line DX10 support? Maybe some marginally faster speeds on various components? DX10 support matters naught if you don't upgrade to Vista, and is only relevant for 2 or 3 games so (including titles in the works).

Your core 2 duo E6600 is still way up there in processing capacity. The newer CPUs have only gained a few percentage points in frequency. I doubt going from an e6600 (2.4 ghz) to an e6750 (2.66 ghz) or e6850 (3 ghz) would result in much difference in actual game performance. Quad core CPUs are almost entirely snake oil at this point (outside of servers and massively parallel data processing applications); IIRC only 1 game actually makes use of more than 2 cores. Going from dual core to quad core will result in worse performance for the vast majority of games and software you will use over the next year or two, or at best no net gain.

Benchmarks will have bigger useless numbers, but real world performance doesn't scale so nicely. Don't buy new hardware unless games (you have already bought) actually start to have performance issues. Its a very slippery slope (approaching frictionless) to start upon.