well, this is an interesting problem
PowerBook G4 17" 1.0GHz
nVIDIA GeForce 4 Go 440 w/ 64MB DDR
512MB DDR SDRAM
My friend has:
PowerBook G4 Titanium 867MHz
ATi Radeon Mobility 9000 w/ 32MB DDR
512MB PC133 SDRAM
for some reason, UT2k4 runs like a bat out of hell on his machine, with all graphics options turned on or HIGH at 800x600 resolution, and with some slight, yet tolerable jumpiness at 1024x768.
on mine, it runs like its wearing concrete boots with all graphics options turned OFF or LOW at 512x384.
this is openGL rendering.
my friend tried openGL (as opposed to DX, which is the default) running on an early GeForce 2 with 32MB RAM and it ran tolerably well at 800x600 with all options turned ON or HIGH
I know the platforms are different between the PC and mac, but both in this case are using the same rendering engine.
what really bugs me is that UT is tweaked favourably towards nVIDIA chips too.