Year2 has some good stuff about passing efficiency in this post.
An outstanding season passing efficiency score is 160 or above. Some years don’t even have a single player reach that level. The majority of players who do hit 160 or above are either seniors or upperclassmen who leave for the pros early. Since 2000, when the NCAA stats archive begins, only 24 players have hit 160 passing efficiency and returned the following year.
It gets lost in the shuffle sometimes, but don’t forget that Aaron Murray was closing in on a 160+ rating for the season in his freshman year (his passer rating before the disastrous bowl game was 162.725). Last season his rating declined to 146.41 due to drops in his completion percentage and yards per attempt and the increase in interceptions. If you compare the game logs between the two years, his 2010 numbers are much more consistent. His second worst rating that year (130.25 against Florida) would have only been his fifth worst effort in 2011.