RE:#6 for SWFF
I know they fish surf perch in California a lot... can't be much fight to that although I heard they are fine table fare.
Searun cutts in the pacific northwest are perfect for a 6wt, although some I've caught gave a great fight on a Spey rod (over 20").
Ocean brown trout in some parts of northern Europe seemed well matched to 6wt rods - based on conversations with friends in Denmark, or Stein's beautiful seatrout posted a while back.
Doesn't seem very useful in the big Northeast SWFF scene, nor down in bonefish country although some areas have predominately small bones (and plenty of them) as opposed to the few educated monsters like down in the Keys.