That 60 FPS is because vertical sync with your monitor refresh rate. Try running Tower57 in windowed mode or Quake 3 without vsync.
You are right! Powermac G5 Quad with X1900 G5 version - Quake 3: 170 fps
AmigaOS: Micro A1-C, AmigaOne XE, Pegasos II, Sam440ep-flex, AmigaOneX1000
MorphOS: Efika 5200b, Pegasos I, Pegasos II, Powerbook G4, Mac Mini, iMac G5, Powermac G5 Quad