I'll probably get chastised for saying this, but I think McCaffrey is a combination of Tim Dwight and Ronnie Harmon. While Dwight had top-notch speed, the difference between him and McCaffrey is the stop-and-go ability, the ability to change directions and accelerate really quickly in his change of pace and change of direction moves.
I also think Ronnie Harmon was a better pass-catcher than Dwight, at least out of the backfield. In Dwight's defense, we didn't get to see him catch balls out of the backfield much as a Hawkeye.
The ironic thing is that if Dwight hadn't gone to Iowa, he would have gone to Stanford. He was pretty wooed by Palo Alto, if I remember correctly.