Completion Percentage. QB rushing touchdowns. QB rushing yards. QB wins. QB starts. I'm sure he's at or near the top for all of these. Any 4-year QB in the modern era will be at the top of most of these categories.
Actually, I found a link (http://www.gophersports.com/sports/m-footbl/mtt/mitch_leidner_793624.html)
He set the record for:
Rushing TD for a QB (career and season)
Consecutive completions: 14 (tied w/ Weber)
Passing yard as a junior
Consecutive 250 yard games (tied w/ 1 other)
Consecutive 300 yard games (tied w/ 3 other)
So, overall I think the big accomplishment is rushing TDs. He does not hold a Gopher record for QB rushing yards. QB wins. QB starts as far as I can tell (definitely not rushing yards though - he is 3rd).