This may be long winded.
I would do this trade, but try to keep Benson. QB's mostly a wash. NcNabb would be the equalizer to TO if you think the team with TO is a Playoff Contender.
Curtis has good upside, but with D.Jackson you would have an incredible WR corp, enough to take you all the way with S. Alexander and S. Jackson as RBs.
Barlow is not doing much anyway. Trade him and pick of Gore, very possible could be SF starting RB towards the end of the year.
If you can not keep Benson I would still do it. You are going to scramble for a back up RB for bye weeks. See if you can get some kind of RB with the trade.
If not maybe you can trade Rod Smith, but with three WRs starting every week Rod could be vauble especially if playing in Mile High, after he has a good week for a running back. However, you running backs should stay health.