There was a time when Peyton looked very different from regular season to playoffs (unless he was playing the Broncos, ironically enough). The stats showed it clearly. More recently he has done better in the playoffs and it isn't so big a distinction anymore. Before the SB though, Marino comparisons were being made.
One thing about Peyton is he seems to oddly lack those super clutch, career defining highlight reel plays that so often become associated with HOF QBs. Maybe I'm just missing some, but what will we see on his highlight reel when we're discussing his HOF induction? I suspect a bunch of TD passes that mostly all look similar, usually in the bland perfection that is the weather of the Indy dome. He made them look so easy, after all.
It's almost like he executes so precisely and perfectly, he has robbed himself of clutch off the cuff moments. Everything is so deliberately planned that it either works like clock work, or doesn't work at all. I recall an article touching on this, and how once the playoffs come around it is very difficult to be an elite QB and an elite OC at the same time - perhaps another reason why the playoffs haven't been as kind to Peyton.
Regardless of his lack of multiple SB wins though, I don't think anyone has done it quite like Peyton. No QB has been this mechanical. Some capture the admiration of fans due to their exciting and heroic play, but Peyton has done it a slightly different way - by being damn near perfect, at least enough to make it practicaly unprecedented, especially in the regular season.