Yearby is too high, IMO. When I saw him live, I was impressed but not blown away.
Don't get me wrong- he is a natural runner and should be a very productive college back. He's efficient in his cuts and instinctive, kind of like a smaller Mark Ingram. But I don't see the unique talent of a Duke, Sony or Collins.
He's probably a 4.6-4.7 guy, and guys like Deon Bush run him down pretty easily on film. Frank Gore and Emmitt Smith weren't burners either, but they were so special in every other facet. I'd rank the South Florida RBs thusly: Sony (assuming he returns to pre-injury form, he has the total package), Collins and then a push between Yearby (better now) and Cook (more upside). I'm not a big Greg Bryant believer.