In particular, what if you want to run Windows 2003 Server as a workstation OS? How does its performance compare to Windows 2k as a desktop OS?
I ran a few benchmarks, after installing the latest NVIDA drivers for my Abit NF-7, which has an AMD 3100+ XP processor, and a Geforce2 MX400 video card. Since it's a relatively low-end machine the results should be relatively slow, but the important question is how they compare between OSes.
Quake 2 timedemo(1152x864, map demo1.dm2) was 51FPS, for both OSes, showing that there's no difference in OpenGL performance.
I tried to run 3dMark, but it would work under Win2k3, so I had to find an alternative.
I found a small benchmark (video-card-stability-test) , which tested DirectX performance. Here the average frame rate was 9, for both OSes. So it appears 3d performance appears identical.
Finally, I found another benchmark called CrystalMark. At first it seemed to suggest that the performance was bit slower under Win2k3, but it turns out that the numbers it returns are relatively variable, perhaps by 10%, even when run on the same OS twice in a row. So a best this is only evidence that Win2k3 is slightly slower than Win2k.