I have a fly for my favorite river to trout fish. This is a softy, tied traditional flymph style, no tail. Hackle is olive partridge. Body is a claret with a bright orange wire rib. Size #14. Doesn't look like any insect on the stream. but this fly will consistently out fish any other fly in my box, on my river, Spring-Fall. I don't know why and it's not just me, having given the pattern to a few close friends, it works extremely well for them. It works only on this river though. To catch fish, that is the fly I grab out of my box, due to experience.
Now to the discussion of body and hook size. I am of the belief, from my experience
that i do better in catching fish by over sizing the hook to the pattern. I like to tie size #16 on #14 hooks. I believe the smaller the pattern the more important this is. I will tie a #20 pattern on a #16 hook. Here is my train of thought. Pertaining to this discussion and "catching" fish. My tendency to tie on a larger hook is not about what the fish is seeing, what I'm imitating, the action of the fly an so on, it is solely on the hooking of the fish. I have caught fish on #20 and smaller hooks. Big fish. I have missed many more than I have caught. I believe I catch more fish by using a larger hook. I believe is is easier to hook a fish with a #12, #14, #16 hook than with a #18, #20, #22. It is more distinguishable the smaller the hook size. For the most part, it works the other way as well. You can use a too big a hook for your quarry, but it is far harder to tie a #8 pattern on a #12 hook. 
As an addition, today there are a lot of hook choices out there. I see many companies offering wide gape hooks now, even on smaller size styles. This wasn't the case a few years back, at least in my fishing circle. I have started to play with sizing the hook to the fly pattern on a couple of the short wide gape styles. One being the Tiemco 111 hook.On fish taking bare hooks and related to my tendency to tie a smaller pattern on a larger hook. I have spent a lot of time, snorkeling water and counting fish. When I was working, I did contract fishery survey work for the US Forest Service. Fish in a lie, whether a feeding lie, holding lie, shelter lie or just cruising in stillwater are constantly pulling items into their mouths. Sometimes spitting them out, sometime chewing them and then spitting them out. There appears no rhyme or reason to what they pull into their mouths. I heard someone associate this with people walking down a trail and kicking stones or pulling a blade of grass and putting it in our mouths. I have no doubt that I have caught fish for no other reason than a fish kicking stones. It had nothing to do with my presentation, fly size, pattern sillouette, color etc. It had everything to do with my hook getting imbedded in the fish's mouth when they tried to spit it out. I believe again, that the larger hook, within reason, will hook more fish than the smaller hook. A #20 is easier to spit out without being hooked than say a #16. Whether the fish is kicking rocks or just realizing that what he has eaten as a BWO is actually a hardened hook with fur and feathers.
Carl
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