it *was* faster before the /console glfaster1 updates.
Now it's at least even if not slightly better. Plus the windows side doesn't support iTunes commands natively. The OSX client has pre-built binds available.
Only issue is if your clan uses Ventrillo and some people REFUSE to use the Speex codec. It's maddening that I have to boot into OSX to use Vent. But that's a personal thing.
Graphics, no difference or better in OSX since updates. That is all.