I think you are giving up too much for Greene.
I think Austin is in for a big year. Before Romo got injured last year, Austin was lighting it up and Dez was struggling. After the injury, it completely reversed. Romo is back, and Austin is going to have a great year.
Greene hasn't proven he can put up consistent fantasy points. He was a big disappointment last year.
I think that a Austin/Williams combination is going to yield you more points than a S.Johnson/Green combination is going to get you.
I would stand pat or look to give up your keeper value and trade M.Williams or S.Johnson for Green.
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