I had slowdown since MorphOS 3.0 with PowerMac G4 andPC flashed Radeon 9500 / 9700 / 9800 (full 128k rom or reduced 64k rom)
All works well now with MorphOS 3.3 even with reduced rom.
PowerMac 3.5, G4 1.0GHz DP, 1GB ram, 80GB HD + NAS, Radeon 9600 128MB Mac, 1680x1050
PowerMac 7.3, G5 2.3GHz DP, 4GB ram, 160GB HD + NAS, Radeon 9800 128MB PC, 1680x1050
Amiga 500+, Vampire 500v2+, HxC Floppy
