Another pretty big (IMO) factor not really being mentioned is Pats finally playing a game with more rest than the opponent. Seems like forever since we've had a rest advantage with this year's schedule and all our past playoff games. (Excepting those Divisional vs. Wild Card Round teams of course). It's usually been the reverse situation for NE in the AFC Championships for as long as I can remember.
Breakdown:
Pats played 3pm ET Sat, playing 3pm ET Sun for a full 7.0 days rest (an extra day, 6 + 1, more than usual Sun to Sun season games).
DEN on the other hand played 5pm Sunday and is playing a bit earlier at 3pm ET for 5.8 days rest, normal sleep recovery, but a bit less a than a Sun to Sun week.
NE goes in with a full day rest and preparation advantage. Manning only gets a normal week but minus a few hours to recover . But let's face it, this year and end of last, he looks best (physically) when he gets 2+ weeks off to recuperate. Not sure if you have noticed how bad he plays with a week or less to rest. So, if last week showed his old ass cranky body rested best, I can only image what he'll look like Sunday... hopefully.