I said this in the game thread, but imagine Fred Jackson taking the field in situations where Choice was out there. Similar change of pace, but much stronger, faster, and more versatile. Spiller will run until he is winded from a big play, then Jackson comes and rams it down the throat of a worn out defense.
I'd love to see the offense run that way with both backs healthy, but the distribution should have been better due to having Choice instead of Fred.