I think it would be wise to kick the tires on Ray Rice. Fred is on his last leg and Dixon is no longer needed as we have a true FB plus hes slow. Bryce Brown sucks. As for Shady, he will gradually wear down as the season goes on. The depth chart would be as follows.
Shady - An East/West runner
Rice - A North/South Runner
Fred - On his last leg, but honorable and serviceable.
Williams - Rodney Hampton in his Rookie season. Can take over next year when Rice, Fred leave.