I think these two points will be key as will consistent play from both running backs. I don't think the factor of Indy's defence showing up or not will be debatable. Indy is a team of hungry guys who have been to the playoffs before and know that the playoffs are like a new season. They will step up. They've got too much of a monkey on their back not to.
For Chicago, Grossman is the big what if factor. He can't even have a bad quarter with Indy's potential for putting up huge numbers very quickly. Their defence isn't an issue, they will do their job and their special teams is clearly superior, but will Grossman not try to win the game and make stupid decisions like he did for the last third of the season? Who knows...