I would definately trade up for Bush. Give them the 2 first round picks and either a young backup O-lineman or a Cooper Carlisle and get Bush.
Will the Cap allow for us to land Bush is the question.
What would we do with our current RB's though. We wouldn't get much for any of them. I'd keep MA and try to deal Tatum for a 4th or 5th. It would be hard to get anything for Bell though when you consider guys like Edge, and Shaun Alexander showed no trade interest last season.