I would go with Plax ... like you said, the Cowboys have a weak secondary, and Plax is going to be Sanchez' big target in the endzone and for long patterns.
best of luck!
and thanks for the help!
QB: J.Cutler, M.Hasselbeck, T.Tebow
RB: L.McCoy, R.Mendenhall, F.Jones, L.Tomlinson, I.Redman
WR: D.Bryant, S.Holmes, Stevie Johnson, D.Nelson, N.Washington