I would keep Benson, he's got some nice matchup coming up including KC in fantasy championship game. Maybe use MJD or Forte to get a better QB, if any managers have top QB as their backup.
I absolutely think you can get Favre for less than Benson. In fact, i would offload any of Bradshaw, Forte, Moreno, Charles before offering Benson, who is tearing it up and looks GREAT! Favre is having a good year, but he's not worth a #1 RB.
Well what I would do is sit down, look at all of your rb's, see what there playoff matchups are, and who has the best matchups for the rest of the year. You are very deep at rb and should be able to make a move for someone. I think a lot will depend on what the teams with two quality qb's have also. If they have two solid rb's then they may not be as willing to make a trade with you. Plus with the way they are playing right now, I would trade Forte before I would Benson. Good luck.
Thanks for the help with mine. I would not do the trade. Maybe try putting a package of some of your other RBs and see if you can get a decent QB that way.