I'm not sure what the deal is, it might just be the age old problem of poor OSX performance with games vs. Windows but my fps in OSX is a good 10-20 lower than when running the game on win 7 on the same system. Is this normal for most people? Are there in fact performance differences between the win, osx and linux versions? Which is generally thought to be the best performer?

Khm... windows 7 is not out officially...

In my experience, Linux with NVidia cards performs the best, but Windows XP is almost as good (no significant fps drops on windows).
ATI cards on the others side can be a major pain in the ass, bacause they have realy bad drivers for linux... so for OSX, that's why you experience lower performance there.

Oh, and I've moved the thread.