I like very large articulated streamers for larger freestone (or tailrace) rivers where large trout but also warm water species are prevalent. For this game, I like articulated streamers in the 3-6" range.
For my local limestone streams, which hold browns over 20 inches, I still prefer smaller streamers, usually in the 2-3" range (hooks sized to match). I've tried the big articulated streamers on the CV limestoners and they will get bit, but smaller flies seem better. In my opinion, this is due to the prevalence of sculpins in the diet of the CV limestone fish. Sculpins in these creeks mostly top out at about 3" with far more in the 1-2" range and I just think that the trout are keyed on this size range prey. By contrast, on the bigger freestoners you have a much wider range of prey species in larger sizes: crayfish, madtoms, chubs, shiners, fallfish, suckers, etc. and big trout and bass are just more accustomed to targeting much larger prey species in the 5-8" range.
It's just a theory of mine, but is backed up with a small bit of personal experience.
