There was an entire thread not that long ago devoted to guessing Wilfork's "actual" weight.
My point actually is that not all players fit into all systems. The Saints biggest complaint about Sullivan was that he was too big and slow to get to the QB, and asked to be taken out of the game too often. The Patriots don't ask their NT to get to the QB (Wilfork got a whole 0.5 sack last year, Warren got 1). The Patriots need somebody with impressive girth to hold up at the point of attack. Furthermore, I have actually watched Sullivan play a couple of times. As big as he was, he was good at filling his hole and chasing the RB to the outside of the line of scrimmage. I have seen him tackle. He wrapped up pretty good to me.
Furthermore, my point is that (if the reports that Sullivan lost 20 lbs at Saints camp this year than) Wilfork and Sullivan's weight are almost identical.