I agree that it can be either water or weather dependent..I fish 1 pond where I will start with about a 6"-8" rabbit strip & may end up with more & larger bass on a size 6 Sneaky Pete....this place is a "bass factory", but you had better have a variety of flies. I have actually caught 4 lb class LM Bass there while fishing size 8-12 flies for gills. I will say that, as stated earlier, I start with the larger flies for bass & that is how I generally do best on the larger bass. Just not ALWAYS.
Mike