DoubleL, you can't compare the Athlon to the P4 clock to clock. I am setting up 3 rigs: high-end Athlon, high-end P4, and overclocked CuMine. I found an XP1600 running 1.55 gig (140 FSB) got a 10,160 3DMark2001 score. A Northwood at 2.117 gig (132 FSB) got 10,671. So the 'little' 1.55 gigger got a pretty good score. Both motherboards were running DDR and are running the same Ti 4600 card.
However that SIS score you got is pretty low compared to mine. The Northwood is running on a P4B266-E (Intel 845D) board, but I am running the Samsung PC2700 at 175 FSB (2600/2550 bandwidth) with the 3:4 divider. I also have a P4T-E rig with 2.3 gig Northwood and that one does 12,661 (at massive 3500/3500 memory bandwidth).
Funny thing is, the XP seens to run 3D more fluid than the P4, even with a lower 3DMark score (and 2000/2000 bandwidth). I am getting better motherboards with volt mods done to get higher on the XP1600. I am going to do more comparisons against the P4 when I get the Athlon up. I hope to hit around 1.6-1.65 gig on it.
But I found there is one caveat to Athlons: they are finicky to overclock. The need a lot of voltage and they run hot. And they are not as stable in 3D at what you think are stable FSBs, so you have to keep dropping it down. Overclocking CuMines are a piece of cake, and P4s are almost as easy.