Tex,
Interestingly enough, Rene Harrop's book addresses the very question you asked (I think). But, first let me say, my comments and Rene's comments apply to heavily fished, famous fly fishing water with Catch and Release regulations - thus the conditioning of the trout to artificial flies.
You mention Frank Sawyer's "Killer Bug". Mr. Harrop, in his book, does address Frank Sawyer's Pheasant Tail Nymph and a variation (with rationale) to it.
His variation:
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