The 6mile carry will about kill you with a full fishing frame.
Last time my buddy took out at prospect, he traded his truck in the next day. The dirt turns real slick when wet.
You are probably better off doing the pickaroon drive; long but very pretty.
There is real good fishing from pickaroon to bennet or from bennet to treasure as well. The former is really a 2 day float, so Bennet to treasure is probably the best fishing day run, but no whitewater.
Keep in mind there is still quite a lot of snow up there, and most of the roads are not good to go.