I start with a 9 ft 5X commercial tapered leader. If I have to go longer. I'll cut it back longer sections of the interval sizes. I like tippets to be 30 - 36 inches at the start and I replace tippet if it gets under 20 inches. I routinely fish 9 ft or longer leaders even on my local streams with 8 ft 4 wt rods. Out west on the Madison I'll go to 12 ft leaders with a 10 ft rod.

On Hebgen I'll fish leaders from 13 to 15 ft. With the cruising gulpers it is hard to tell where they will be next and you need the fly far away from the line to prevent the line falling near the fish you are after. If your line gets near a fish on the cast you will see the wake of fin spash of the fish when it spooks and then you know to lenthen your leader.