Does anyone know if there are recommended guidelines regarding the weight of the fly (Streamer mainly) you are casting and the recommended wt. of the fly line. That is, are there certain lines and tapers that will work better with heavier flies.

I am casting pretty much large streamers with bushy maribou tales -- fly wt. is 15 to 20 grains. I can't seem to get any distance using an 8 wt. rod. Maybe with a bass taper??

Anyone have any ideas??