Fantasy football trade proposal: RB C. Johnson for RB R. Mendenhall & WR P. Harvin?

I'm in a fantasy league of 6 teams with some friends and have Mendenhall and Harvin being offered to me for Chris Johnson. The league has 2 rb 3 wr and 1 rb/wr position to fill. My running backs are CJ, Jones Drew, and Brandon Jackson. My WR's are Greg Jennings, Hines Ward, Santana Moss, Austin Collie (injured), and Hakeem Nicks. Even though Mendy and CJ have almost identical fantasy points I feel like CJ is due for break out games with the addition of the deep threat Moss. However I could use the addition of Harvin to improve my weak receivers group. Should I accept?