From what I've heard, the biggest problem is when you have the nagging injuries late in season, a 5 hour flight sucks ass. Being couped up on a plane and not being able to use team facilities as much is what has the biggest impact on whether players are 80% or 90-100%
They don't fly coach.
The bigger issue is health. Winning on the road in the playoffs, no matter how many consecutively, isn't an issue. That was an extremely physical game, and the QB is far less than 100%.