3DMark is mostly meant to measure how good your PC is for playing 3D games (it's made by Remedy, a games company and ex-demo crew), so the speed of your CPU will affect scores. Most of my current CPU knowledge comes from the PC world, unfortunately (back when I last looked at these things on the Amiga, a 68040 was the high end), so I can't tell you how this maps to PCs. I've heard claims that an 2x MHz P3 = x MHz G4. I suspect it's a bit less than that, but I'd be surprised if a G4 were slower than a P4 running at the same clock speed. It's hard to compare the two because Motorola goes for lots of shallow pipelines, whereas Intel likes using just a few very deep ones. I guess the only reliable benchmark in such a case would be to compare the same (modern) program on x86 and Mac, for example Quake3 framerates for x86 vs Mac would be a good reference (is there Quake3 for the mac?)