How much is Tebow overperforming?

When Total QBR was introduced before the season, the interpretation provided was that on a game level, Total QBR is a 0-100 number that represents the percentile ranking of how good the quarterback's game was compared to all other QB games from 2008 to 2010. So if a QB finishes with a Total QBR of 80 in a game, his performance in that game ranked better than roughly 80 percent of all QB games in that time.