Win, I can see Frank playing another 4 years, but only if he starts sharing the duties significantly in a couple of years. He generally logs over 225 carries a season (sometimes significantly more), and he'll have to trim that to well under 200 in a couple of years. I agree with you that Frank is running better than he has in a while, but that doesn't mean his body isn't taking a pounding from all of that running between the tackles.