A guy on footballguys.com has done an analysis of RBs based on just 3 things: age, weight, and draft position. He splits them into 9 groups based on these factors and the groups are pretty interesting.
As an example, group 1a is backs from 205-221 lbs, under 22.5 at the draft, and first 76 picks OR under 22.5, first 15 picks. In the last 10 years this consists of:
Clinton Portis, Edgerrin James, Maurice Jones-Drew, Marshawn Lynch, Reggie Bush, Ahman Green, Laurence Maroney, Brandon Jackson, Kevin Jones, Thomas Jones, Jay Graham, LaDanian Tomlinson, Frank Gore, Adrian Peterson, Darren McFadden, Felix Jones, Kevin Smith
As you can see, group 1a is some very nice company to be in.
Jamaal Charles is in his group 2b which is the same as group 1a, but with a near-miss on either age or weight (Charles was under 205 lbs).
This group consists of:
Brian Calhoun, Maurice Morris, Byron Hanspard, Moe Williams, Tiki Barber, Ladell Betts, Michael Pittman, Julius Jones, Michael Bennett, Joseph Addai, DeAngelo Williams, Ray Rice, Jamaal Charles