I did a lot of benchmarking of Quake III in last two days and here are my results:
All tests were done on Morphos 3.0 with TGLSYNC 0 and r_primitives 2, all settings maxed out (32 bit textures and rendering, max textures and geometry, trilinear filtering):

Mac Mini 1.83Ghz Radeon 9200 64MB:
512*384 104,8 FPS
640*480 75,4 FPS
800*600 60,0 FPS
1024*768 42,7 FPS
1280*1024 30,5 FPS

Mac Mini 1.5GHz Radeon 9200 32MB
512*384 93,0 FPS
640*480 68,9 FPS
800*600 52,6 FPS
1024*768 28,8 FPS
1280*1024 4,4 FPS
On this Mac I was expecting better performance in 1280*1024 when it gets out of memory (because of new driver and swap mechanism) but actually it was worse than with MorphOS 2.7. Also 1024*768 was worse.

And finaly results from Mac OS X port of IOQuake III 1.36 on Mac Mini 1.83GHz Radeon 9200 64MB:
512*384 123,0 FPS
640*480 116,8 FPS
800*600 90,3 FPS
1024*768 60,8 FPS
1280*1024 40,6 FPS

I also noticed that I can't use 320*240 screenmode in Morphos 3.0 (I get black screen) while it works in 2.7.

Actually I could achieve over 140FPS but in 640*480 or lower on lowest possible settings. I would really like to know how someone managed that on Mac Mini in 800*600...