My 2600XT 512 MB card gives me worse scores then before with my integrated GMA950 glitchy graphics in Xbench... do you know why? I use the lastexile ktexts....

Forget Xbench OpenGL values - they are wrong.

If you test, use the OpenGL Extensions Viewer , it has an Bench included. Activate the option BENCH + option Fullscreen and test in an higher resolution with 32 Bit.

Xbench values of my ATI HD 3850 (up to 2,5 times faster than 2600XT) are also "BADer" than GMA 950 !

I added my results of my "old" 2600XT. If you use smaller res you will get a bit higer results.
GMA will performe here less than 20% of your card !!

Best tool to test OpenGL performance is OpenMark
Place mouse out of OpenGL window!
You also can take CineBench (google for it) and compare performance in MacOSX and Windows. Usually Windows is 20% faster.