Allan, I was on Penns Creek this summer and there were some absolutely huge March Brown spinners around. The fish weren't quite on them yet, but I hear that when they are it's gangbusters. So there is another argument for some BIG flies. The Brown Drakes and Green Drakes on Henry's Fork are another. It is a shame that we don't have readily available sources of big hackle. Even tailing on regular size flies is a real problem, and I've gone to Coq de Leon.
Eric