TFL and PBU are good, but there aren't stats for Missed Tackles, Passes Completed On, Missed Assignments, etc. I am not meaning that to rip on Bills, just that I feel Sorenson had better skills, instincts, etc and truly understood his assignments to a greater degree, and knew better how to get defensive backfield into position. However, I can't offer much more than just what I personally saw watching games and replays.
In Bills' defense, Sorenson had a MUCH better pass rush to support him and allow him to get into position better. That should count for quite a bit.