I don't think you have a choice but to upgrade at RB and do it while Martin's perceived value is still high. Mathews has never had a truly stellar season - he's injury prone, and he's way overrated. Both RBs have limited upside and very big downsides. It's a great weakness to have in a scoring format like yours, so what you need to do is target some pass catching RBs who aren't flashy to get you some consistent points while Brees, Gates, and Welker rock your face off every week. Don't give up your pass catchers or any of those 3.
I'd test the waters to see if someone is stupid enough to trade a Forte type RB for Mathews and Martin paired. Otherwise, go for a McGahee type, or Sproles, or SJAX... someone along those lines. OR, even better, see what you can pick up off the wire - guys like Gerhart, CJ Spiller, etc are all out there in a lot of leagues and have some upside.
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