I think the Broncos can do it. I've said it all year, there aren't really any "Super Bowl" defenses out there when compared to past years. The NFL is watering down every year it seems like.
Denver and Pittsburgh are about as good as it gets. Carolina on a good day, they seem to be kinda erratic though. I think Chicago and Tampa Bay both had the two best typical "Super Bowl" looking defenses, but they're gone. Denver and Pittsburgh live and die off the blitz. Neither team is exceptional in coverage... but one of them is going to get to the Super Bowl. Maybe defense is dying in the NFL.