Let me put it this way, if the person in your league is stupid enough to let you have two of the top RB's and upset the balance of your league then go for it. If you don't run away with your title then something is wrong.
It really depends on your depth at both positions. If you are strong at receiver and weak at running back then do it. Otherwise, you are giving away 2 top 15 receiver's for the best RB. But I don't feel it is worth it unless your RBs just suck.
I play in a PPR league. Would you guys accept a trade that was julio jones and jordy nelson for lesean Mccoy. Or julio Jones and larry fitzgerald for lesean mccoy. I am getting Mccoy in both of these trades.