Jamo,
I tie Rangely style streamers and bucktails on Mustad 6x long hooks up
to size 6 (78950?) and have no trouble handling them with either my
Orvis 5wt (8-1/2' Henry's Fork) or my St Croix 9' 6 wt. The thing is,
I'm fishing small to mediums sizes streams where 50' is a long cast,
and much of the fishing is accomplished with roll casts. Fishing
requiring longer casts could change the equation.

Most of the Rangeley designs were originally intended for trolling, and
were tied on the longer (8x+) hooks, or with a stinger hook. These
patterns have been adapted quite well to the somewhat shorter hooks for
stream fishing, and they are still favorites for fishing in northern
New England. I fish them deep, so I favor a heavier hook. One tip. If
you're tying with traditional feather wings or marabou, keep the wings
a bit short, or add a small bunch of bucktail between the body and the
wing to keep the wing from wrapping around the hook during casting.

I'll bet Peter Charles will have some valuable info on this subject.