Have you ever read "The Hidden Game of Football" by Pete Palmer, Bob Carroll, and John Thorn? They did some of the first comprehensive SABR-metric stuff for football, charting NFL games about 20 years ago. Their basic benchmarks of success were as follows:

1st Down: Gain 45% of the yards needed for another first down
(1st and 10, gain 4.5 yards; 1st and 15, gain 6.75 yards, etc...)
2nd Down: Gain 60% of the needed yards
(2nd and 10, gain 6.0 yards; 2nd and 5, gain 3 yards, etc...)
3rd or 4th Down: Gain 100% of the needed yards

Aaron Schatz of Football Outsiders built on those concepts and created a more refined set of benchmarks for every situation (down, distance, time remaining, ...) for his advanced NFL play-by-play metric, "DVOA": http://www.footballoutsiders.com/info/methods

The college play-by-play stuff on FO has been mostly developed by Bill Connelly of the Missouri blog Rock M Nation. For an answer your question if not the answer, Bill defines basic success rate as 50% of needed yardage on first down, 70% of needed yardage on second down and 100% of needed yardage on third or fourth down: http://www.footballoutsiders.com/varsity-numbers/2008/varsity-numbers-ncaa-analysis-101

These benchmarks pretty much align with your post.