3DMark (as the name hints at) is NOT so much a CPU benchmark, rather a GFX-benchmark.
For P4P's you get about +100 points for every 100 MHz (-ish). So, you can get a few more points purely that way round.
The BIG difference (say 1.5 K points per generation) is the graphics card. To move the same amount of points that you
get when you move from GF3 to GF4, you have to get 1+ GHz in your CPU.
The CPU is more a "icing on the cake" in 3Dmark - it's down to your graphics card mostly.
As such, your question is rather ill-placed.
Hope this helps.
- Shathal.