Interesting feedback. I guess I should have pointed out that the most recent cases the breakage has occurred on the first fish/hit of the day, so it has not been a case of post-fight abrasion. I had not really thought about imperfections in the metal of the hook eye, I suppose that could play a part, but my gut sense was that these were impact related. Funny thing is that I had heard other people complain about this with these knots and just shrugged it off the last few seasons because it never happened before.
I guess my point is that I am losing confidence in this knot unfortunately. Maybe stronger tippet is the answer, or higher quality hooks. I just don't like losing fish and I do like the free swinging fly, particularly for dead drifting in curents or rips (good side to side motion).
Tom, I have nothing against 20 lb. per se, I just prefer 12 or 16 in certain applications.