Helu is a bust, toss him. Shanahan is too flaky to rely on any one at the RB position, its just simpler to go with someone more reliable, even if they don't manage to get that one big game.
Id seriously consider using Newton as trade bait to get yourself some better WR's. Brady has a MUCH easier schedule coming up, and both Brady and Newton face Indy, so thats a huge game for both either way. You can probably get a stupid trade for Newton since everyone loves him.
Id probably play Ben Tate over Roy Helu unless some waiver wonder is still around (DeMarco Murrary or someone like that). Take a look at Earl Bennett from Chicago. Hes been pretty solid thus far in his last 2 games, coming back from Injury.