Could you imagine the numbers Kelly in his prime would put up in Chan's offense? Not to mention in this new generation of football where DB's can't touch WR's. I'd go as far to say Kelly would annually throw for well over 4,000 and 35 tds...EASY. Guys like SJ, FJ, and CJ would be killers. If everything remained the same on the 2012 Bills and you simply replaced Fitz with Prime Kelly the Bills would be the SB favorite, in my opinion. This offense is tailor made for Kelly's skill set and his ability to read and react. I'd argue that Tom Brady would be the second best QB in the division.
Anyway, one can fantasize.