BlkKnight put up a web page showing user submitted Doom3 benchmarks.

It's only been up since Friday and we've had over 6000 hits and 200 results.

The page realistically shows what you can expect out of "normal" gaming rigs.

Useful things we've seen:

If long as you have more then 512 Meg RAM performance will not be affected my memory.
If you have a CPU rated over 2500 performance will not be adversely affected.
The FPS gains are purely in the video card.

Check it out