Eric "the Great" Dickerson was the fastest of the top RB's of his era---faster than Barry Sanders. I believe he has done at least a 4.3 40, but with his upright running style he never seemed to be going quite that fast. When Eric hit the pile, the whole pile would surge forward for 4-5 yards before he was stopped, like primetime Larry Csonka. When Eric was in full stride in the open field, you couldn't tackle him high: he simply ran through arm tackles like they weren't even there.
Marshall Faulk could have been a star as a receiver: his hands were that good. He truly was the X-factor for the GSOT. Great vision, ability to read defenses like a primetime QB, and utilize his blockers. He was often unreal at picking up blitzes, and was a super reliable bail out option when the primary/secondary/etc. receivers were unavailable. Legitimate 4.4 speed entering the pros, he could embarrass defenders and DC's almost at will in his prime.
Top RB's are like elite artists. It's hard to determine who is best as they each have their unique styles. I appreciated both and am glad both grace the field for our Horns!