As the title says really, Xbench shows no difference in performance either.

Anyone know why? I was under the impression that the BIOS controlled the CPU frequency but it appears as though OSX is doing it.

that sucks ;-) what kernel are you running? what are the specs of your system? this info helps ;-)

ive had the same issue with a P4 it is 3Ghz and Osx claimed it as 3.6 Ghz, i was using the old kernel. after i changed to 10.4.8 kernel it stopped reporting it incorrectly. Your Hackintosh isnt running any slower, its just being reported incorrectly

Its really running on that speed, your kernel does no auto detect the right FSB, you have a 266Mhz fsb cpu, but it runs with 200Mhz fsb. So get a new kernel!

you can boot with fsb=267 -v
thats what i do just before i boot