Old thread but...I've found the size of the stream doesn't really matter, it's the character of the stream, the vegetation surrounding it, and/or the way you want to fish it that influences rod length. A creek that's a tunnel through brush and overhanging trees may be best fished 6' rod or even shorter. The same sized stream in the open with brush lined banks may be best fished with a 9' rod casting over the brush.
I haven't really kept up with the fly fishing market but in recent years, some of the bargain rods and lines I've cast here and there were surprisingly good. It's a good time to be getting into fly fishing.
