Well, like I said in a previous thread, Darren is kinda unique. Believe me, he isn't Payton or Adrian Peterson, look at the game film, he is alot different. Those guys are very physical in all their runs, using alot of power and balance.
Really, the guy he looks the most like is the Razorback whose rushing record he broke, Madre Hill (of course the record for Madre was in less games). Hill had 3 knee surgeries that slowed him down, but Hill was a legit 4.2-4.3 RB before the injuries, and the film would tell you how much they are similar if you are familar with them both.
As for backs in the NFL, well, Darren breaks angles everywhere on the field. DBs and LBs always take the wrong angle on him and it causes Darren to get hit less than most backs. He also has the strength to hit someone if he needs to. Really, I don't think there is a comparison, LT isn't a comparison cause LT uses more lateral movement. Larry Johnson is not as fast but more physical.
Only person I can think of is Eric Dickerson, although they look different when they run, the results of their runs look very similar when you look at what they do to DBs and LBs. What needs to be understood is there is a difference in top speed and the 40. Eric probably wasn't all that fast in the 40, but at top speed, no one could catch him, same goes for Darren. OJ Simpson is also a good comparison. Darren is in for a big test this year, the Hogs aren't really as good and the schedule is alot tougher. Don't be suprised if he doesn't have as good a year, but he will be featured in the offense, so the numbers will probably end up being there again.