There's also a huge difference playing the Steelers in Pittsburgh as opposed to Denver, especially since the Broncos were banged up in the secondary when they played. As long as Peyton doesn't give it away (a distinct possibility), they should win that game.
The other factor in that Pitt game was Brock's inability to adjust when Pitt's D went into a zone read. The Denver offense vanished in the second half largely due to Brock's inexperience reading that type of defense and/or the limited playbook he had at his disposal due to his youth. I don't think Manning would be quite so deer-in-the-headlights in that situation. Pitt is also potentially missing Deangelo Williams so their running game (which Denver was able to squash last time) could be weaker than they want.
I'm not terrified of playing Pitt. They definitely could beat us again with their high flying pass game, but they also lost to Baltimore 8 days ago, so who are they really?
I think all 3 potential Denver opponents could be trouble or could be beatable.
Pitt is outlined above.
KC beat Denver at Mile High this season and (as GF pointed out) nearly beat us earlier in KC were it not for a lucky fumble bouncing into a TD return. They are hot as can be and have a stout D to go along with an increasingly solid passing game with Alex Smith playing the best ball of his career. On the other side of the coin, their big win streak hasn't exactly been against top opponents. During the 10 game streak they beat: Pitt, Detroit, Denver, SD, Buffalo, Oakland, SD, Baltimore, Cleveland, Oakland. Only 2 winning teams in that stretch and 3 of the last 4 games were won by thin margins. Are they more of a paper tiger than the big streak implies?
Houston only beat two teams with wining records in their 9 victories (Cinci and NYJ) and they are thin at RB and receivers behind Hopkins (Washington, Shorts and Griffin aren't scaring anyone on their own). Their QB situation is shaky and I don't expect Denver's D would have too much trouble with them. That said, the thought of JJ Watt and Jadaveon Clowney blasting past Denver's shitacular OL and crushing the passer will keep me up at night if they end of being the match-up.
I think KC is probably the team I would least like to see, but bring them on if that's the way the cards are dealt.