Re: casting a 5wt?
As usual Frank has nailed it pretty well. My experience (which doesn't include salt water but just fresh water trout/salmon river/stream/lake wading/tubing) with my vintage 7'7" Scientific Anglers System 5 fiberglass, my Sage 8'9" 5-wt. SP and my Sage 10' 7-wt. XP, as well as a borrowed 8-wt. in Alaska for salmon, has been that the same style works with all of them. The major difference to me is not so much in line weights but in the action of the particular rod, from my slow S.A. fiberglass to the medium flex of the Sage SP to the fast Sage XP. I guess I would add that in windy conditions (no stranger to you on saltwater, I am sure), the 5-weight will be more difficult to project out than the heavier rods you are used to using.
On the whole, I'd rather be in Wyoming . . .