FYI...

I was using BIAB windows on my iMac (running XP) and found an occasional studder in playing - due to the overload on the processing time but, otherwise, my older version worked nicely. But, I switched to the Mac version to avoid running Windows. Now, even with the few bugs/annoyances yet to be corrected (and I'm sure they will be), running the Mac version is great (the only significant shortcoming, in my opinion, is the absence of the Jazz Fakesheet, the Lyrics window and default of Overall Loop on).

I'd go with the Mac version without question and best of all is the easy drag and drop of the file into GarageBand (works just like they advertise!).