Usually, backs that are high volume rushers have lower yards per carry. Peterson didn't play in a one dimesional offense. And when I say one dimensional, I am being kind to the Bengals. I watched every Bengal snap last season and after Henry went down, the offense was as predictable as it gets. Knowing they didn't have the protection to hold the ball and go deep, Marvin became content to get a lead and squeeze the air out of the ball.
Compare Peterson and Benson against common opponents. Top performance against divisional opponent included.
Peterson
GB - car. 25 yds. 97 ypc. 3.9
PIT - car. 18 yds. 69 ypc. 3.8
BAL - car. 22 yds. 143 ypc. 6.5
Chi - car. 24 yds. 94 ypc. 3.9
DET - car. 18 yds. 133 ypc. 7.4
Benson
GB - car. 29 yds. 141 ypc. 4.9
Pit - car. 17 yds. 76 ypc. 4.8
Bal - car. 27 yds. 120 ypc. 4.4 (first back to break Bal's 40 game streak of not allowing 100 yd. rushers)
Chi - car. 37 yds. 189 ypc. 5.1
Det - car. 36 yds. 110 ypc. 3.1
Add to that, Chris Henry went down 11/8 during the second Baltimore game. Up until that point, when the Bengals had that vertical threat Cedric's numbers look like this
car. 198 yds. yds. 837 ypc. 4.2 24 carries a game
Now extrapolate that over the course of a full seaon and you come up with:
car. 396 yds. 1674 that would have been good enough for #2 in the league
Not arguing that Peterson isn't an elite back, but Cedric Benson not even being in the top ten after a primetime performance like that?