It seems that the MacOS version is happy with a 500Mhz powermac
You're right. I remenber playing RTCW on Mac OS X (Power Mac G4 450 MHz with Radeon (7000 ?)) some years ago. The animation was smooth but I can't remenber the resolution. Perhaps it was a simple 640x480.
Here with MorphOS 2.7 on Power Mac G4 1250 MHz and Radeon 9100, the game is smooth in 1280x1024 with max settings. However, this game is a bit more slow than Quake 3.
Obligement - L'Amiga au maximum