I fish for bass (mostly smallmouth) more than trout. My go-to rod for the past several uears has been a 8'6" 4wt. My experience is that you don't need to toss huge flies to catch bass. In fact, the largest hooks I own are #10 Tiemco popper hooks that I use for Clouser Minnows, and some 4X Long streamer hooks in size #6. I tie my Clousers with bead chain eyes, or 1/40oz lead eyes. The heavier flies--dry or wet--are easier to cast with 3X leaders, and I tie my own at around 8 1/2 feet. That's short enough to turn over something heavy, and long enough to keep the fly line out of the fishes' sight.
post the pic of the 25" LMB I caught in 2009 on a #10 Wooly Bugger, but it's been posted here too much.
I just got back from fishing the local stream with my 4wt, and was using a #10 Wooly Bugger. I was standing in a shaded portion of the stream, and spotted a smallmouth that had to be 18 inches. It was 20 feet away tops, and I cast the bugger right in front of him. He half-heartedly took the fly, and I set the hook with glee! The battle was on, but he spit the hook after a minute or two. I was just aamazed that he took it at all: he seemed to have seen me, but maybe being the shadows helped. In any case, he was a leaping fool, and that's all I needed for today.
I've been catching 10-12 inch smallmouth on #14 Gold-Ribbed Hare's Ears this year, and that just confirms my strong belief that you don't need a big fly for bass. I haven't mentioned the smallmouth bass marathon that I had in April and May, because I switched to a 9' 5wt. These were FAT 16-19" smallmouths, and using the 4wt would have made turning these fish in strong currents too much. The flies I used were the same #10 Clousers and Wooly Buggers, so nothing different there. My top side bass fly is a green foam bug I make from foam door knocker material at the local craft shop. It's tied on a #6 Tiemco standard wet hook (strong wire and wide gap). I also use Madame X flies tied on the same hook, or smaller. They both work equally well, but the foam bug is quicker, and never needs floatant.
Here's a thread I started this time last year: Why Are My Biggest Fish Caught on Small Flies?
9' 5wt rod, but same old #10 Clouser Minnow (April 2012):
I can't help myself, so here's the 25" LMB from 2009. The #10 Wooly Bugger can be seen in its mouth. I was there for stocked trout, so this was a surprise.
The #10 Wooly Bugger in the vise: