Unreal Tournament
The difference is rather small, which shows once more that Unreal Tournament doesn't agree that well with Pentium 4 or RDRAM.
Under Windows 2000, Intel's 850 chipset and its RDRAM can leave P4X266 a bit further behind, but we are still only in a 5 -7 % range.
3D Mark2001
It is interesting to see how different this benchmarks behaves under Windows 98 and Windows 2000.
While under Windows 98 the scores of both platforms are high and pretty close to each other,
the differences between the two contestants get rather huge under Windows 2000, but both contestants score pretty sad overall numbers. I guess that the latter score is close to negligible, because the majority of gamers are probably still using Windows 98 or Windows ME.
More about chipsets
