Pretty even trade. I don't think I would do it though due to the risk at your QB position.
While you will get a little bit of a bump in both RB and WR, you are taking a pretty big chance at QB. Big Ben is a low end QB1, but has proven he can do it year in and year out. Not much risk and you know what you are going to get. Freeman is a bit of a gamble. He played well last year and has promise and could give you a good year, but you are taking a chance with him. I think his top end if he has a good year will be that of equaling Big Ben. If he struggles, your bench QB (Sanchez) isn't going to carry you. So I am not sure that the bump that you will get at RB and WR will out weigh the risk you are taking at QB.
10 team, PPR, 1 qb 1rb, 2wr, 2flex (rb/wr/te), 1k, 1dst
QB: Stafford, E. Manning
RB: Peterson, Blount, Hightower, Starks, Tate, Tolbert
WR: Nicks, Wayne, Bowe, S. Johnson, M. Thomas