The CPU sure, but I'm wondering how usable the graphics card would be, it not being one of the graphics cards that ships with a Mac. It'd suck having am lack of drivers be a bottleneck.
If you're willing to spend a bit of time following a guide to set it up properly, your performance shouldn't be much worse than the cards that ship with real Macs. Comparing with Windows, games performance is pretty average (on par with genuine Macs) but I have no trouble with video playback, window draw/effects, and even 3D work in Silo.
