I think it's been pretty well proven at this point ... if you can get an early lead on the Pats, Mac struggles to bring them back. Think the way the Pats are built right now is to play with a lead - where they can just run, run, run.
I think the Bills will have their hands full in this one, but if they get a 2 score lead, I would expect the pass rush / defense to just be too much for Mac. He should eventually be a decent QB, but he's just not there yet.