I think it's more of what you are comfortable with than anything. Myself, i usually take as long a rod as possible, even on very small streams, just because i like having the extra length to get the fly out there and high stick. I would think that a 9' is the best length, overall, for the smokies. If you don't feel comfortable making that big a jump then go smaller, like 8'6" or even shorter if you like. Just stop by LRO and try some out that way you can feel how several different ones feel.