I've been using AMD/ATI HD4870 on Kubuntu x64 for a while now, and then I decided to try out (borrowed) NVIDIA GTX 260 - which is a slightly worse card (on Windows). I also tried NVIDIA 8600 GT which is a quite crappy card.

The results were quite sad, and I'm considering that I failed (Multiple times? Seems odd.) with the AMD/ATI drivers. Please note that glxgears isn't much of a benchmark, but it does show me something.

fgl_glxgears
5500 FPS NVIDIA GTX 260
2100 FPS NVIDIA 8600 GT
2200 FPS ATI HD4870

glxgears
110k frames / 5 seconds - GTX 260
40k frames / 5 seconds - HD4870 and 8600 GT


Here sure is a big difference.

I also tried Wine World of Warcraft, which resulted in about 2-3 times more FPS on GTX 260. And the FPS on 8600 GT was as good or better than HD4870.
I did try a small particle OpenGL program I wrote, which resulted in about two times more particles at higher FPS - on both NVIDIA cards (CPU bound) compared to HD4870.

Do anyone else have any experience using ATI and NVIDIA? It feels like the performance on ATI should be better than this - or is this a common problem?
I'm right now considering buying a NVIDIA Fermi card (as soon as Coolbits is working, and ETA yet?).

NVIDIA Drivers:
256.53
ATI Drivers:
10.8, 10.7, 10.5.