I have the 9′ 6wt Scott S4 and someone will have to pry it from my cold dead hand to get it. Honestly, I fish the 6wt class more and more each year for medium sized rivers. I have casted the 9′ 4wt S4 and it is every bit as good as the 6wt yet lighter. The 6wt S4 is my go-to rod for streamer, warmwater and light weight saltwater fishing. Great rod if money is no option.
FYI/BTW, I have an 8’6″ 4wt Z-axis which, IMHO, is similar in fast-action to the 9′ S4. What I have found is that it tends to be a bit short for nymphing and a bit too fast for dry fly fishing. Ergo it tends to stay in the closet.
Just to throw a wrench into things . . . my new favorite 4wt rod is a 10′ 4wt from Orvis. It is the perfect length and weight (actual weight in hand, not line weight) for long days of nymphing and wet fly fishing. I believe the Europeans are way ahead of us on the longer rod game and over the past year I have come to believe in the benefits of longer lighter-line-weight rods. However, you mentioned smaller streams – the longer rods may not be a good match for your needs in this case.