I don't do much freashwater fly fishing but my saltwater flies vary from 2" to 9" long. I use a TFO TiCRX in a 9wt which is a fast action rod. I've noticed that if I line up (10wt) the big flies throw better for me. More importantly, don't rush your cast A heavier fly needs more momentum and line speed. Most casters think they have to push hard with a heavy fly. The exact opposite is true, concentrate on lifting it smoothly, go slow, watch your loops and get the most out of the line speed your rod tip creates. Hope this helps...