Bass are aggressive opportunistic feeders. I say again, aggressive. Catch them in the right mood, and they will slam a popper on top and slam a clouser minnow stripped fast under the surface - regardless of size. With that said, I agree 100% with the statement "...castability is the priority...". If you cannot affectively present the fly in the correct spot, size won't matter.

I once caught a 4 1/2lb bass on a 4wt casting a #10 woolly bugger(ish) fly. Crawfish color, dragging it on the bottom, and bingo! Fish on!

Whatever you do, tie patterns that you can cast efficiently, effectively present, and have fun with.