The fact that we are looking at RBs tells me that McGahee isn't 100%. He hasn't looked 100% the last few weeks (since he got hurt). He hasn't run with the same authority or burst he had earlier in the year and seems to be dancing a little more instead of pressing the hole or making his own like he had been doing. On the few carries where he does run hard, you can see him get up slowly and typically comes out of the game for at least a few plays. I think he's still nursing a hammy.
I wouldn't mind seeing a little more of Jeremiah Johnson. He obviously catches pretty well out of the backfield (about the only time he sees the field is 3rd and long) and supposedly he was one of the better RBs in camp.