I use a 4wt for almost all of my trout fishing in the lower 48. A 9ft 4wt is a perfect nymphing or dry fly rod for most water. I prefer a 6wt for streamer fishing for trout. The rod flex matters on the 4wt. Too stiff and it is not much for roll casting and dry fly presentation. Too soft and you cannot turn over split shot and indicators as easily. A 7 wt is best for AK larger rivers. A saltwater 6wt with a small butt and some flex would be the ultimate for big rainbows in most other streams. I have fished a 4 and 5 on Bristol Bay streams and they were a pain fighting the fish. Was not enough backbone to turn big fish in the current. This is experience from 10+ years ago. I understand that there is now a big contingent of folks in AK that fish Spey rods on big rivers like the Naknek and Big Ku. I ran into a bunch of Naknek guides who were Spey fishing for Roosterfish in Mexico. Go figure.
