if it doesn't run well in windows, the UB won't help. the UB has some really strange slowdowns with grenades and explosions - the windows version is more constant.
if you care, here's the timedemo for my macpro with the UB.
Date / Time: 12/13/06 8:51:56 (0ms)
2700MHz, 1024MB
C:\Users\eldunko\games\Halo.app psn_0_3145729 Frames=4700
Total Time=51.40s
Average frame rate=91.43fps
Below 5fps= 13% (time) 0% (frames) (6.891s spent in 10 frames)
Below 10fps= 13% (time) 0% (frames)
Below 15fps= 13% (time) 0% (frames)
Below 20fps= 14% (time) 0% (frames)
Below 25fps= 14% (time) 0% (frames)
Below 30fps= 17% (time) 1% (frames)
Below 40fps= 22% (time) 3% (frames)
Below 50fps= 23% (time) 3% (frames)
Below 60fps= 27% (time) 5% (frames)
###Sound Options###
Hardware Acceleration= No
Sound Quality= Low
Environmental Sound= No
Sound Variety= Medium
###Video Options###
Resolution= 1024 x 768
Refresh rate= 0 Hz
Framerate throttle= No Vsync
Specular= Yes
Shadows= Yes
Decals= Yes
Particles= Off
Texture Quality= High