I have a 333 iMac and a DP G4 450. My old Que USB CDRW worked fine burning at 4x on the iMac but no go on the 450 - even at 2x speeds most of the time.
Low and behold, after I updated to 9.1, I tried it out - made 5 perfect CDs at 4x on my G4 - OS 9.1 saved me $300 on a new Firewire CD Burner!
-s'fit