I think you answered your own questions. I think it would help if you listed their oppositions.
Pierre Thomas (NO) vs. SF
Brandon Jackson (GB)* vs. BUF
Ronnie Brown (MIA) vs. @ MIN
Darren McFadden (OAK) vs. STL
IMO, I would start Thomas and McFadden. Like you mentioned, the Rams D is atrocious and Michael Bush will prolly not play again. As for Brandon Jackson, he's an average RB and John Kuhn might steal the goal line carries away from Jackson. I would need to watch a game and make an evaluation to see how Jackson really fairs.
I wouldn't drop any of your RBs for any of the WRs that you listed. RBs are way to valuable in fantasy football and you have guys that will prolly do well on a consistent basis. WRs are a dime a dozen and I think you're making a haste decision after only week of games.