McCoy won't have the benefit of a Chip Kelly or Andy Reid offense here. He also won't have a dominant run blocking offensive line like he had for most of his career in Philly. Look at how the other RBs have done there in that time...even the past two years with Bryce Brown and Darren Sproles. McCoy is a good player, but he won't be putting up those kinds of numbers here. He's not a punishing runner. He needs to get to the second level to do most of his damage. The guy dances around in the backfield too much and he won't get away with that here. He's a better version of CJ.
On the other hand, if Greg Roman really is an upgrade to Marrone's cluelessness (and how could he not be?), I think Fred Jackson will benefit most from it. Everyone is quick to say he's lost a step, but not only was he playing hurt last year, but he's never been the burner type anyway. McCoy will get more chances because of his name, his contract and who we gave up to get him, but by the end of the year, Fred will again prove to be the best RB on the team.
Yes, he's getting up there in age, but take a wild guess as to who has more career carries between the two.