The Simms Riffle Jacket is as solid a non-Gore-Tex jacket as we have seen. It is breathable, dependable in the rain and good looking to boot.....
Is it enough jacket for a week long float trip in Bristol Bay? Depends on the weather. If you get a fairly normal week of decent weather with rain here and there, then yes it will do the job just fine.
However, if it rains for multiple days in a row you would be better off with one of Simms higher end jackets such as the G3 Guide Jacket or G4 Pro Guide jacket. They are built to shed water for a longer period of time and keep you dry in really adverse conditions.
If you can squeeze it in the budget, you'll never be sorry you bought a better jacket!