In my opinion adding weight to any wet fly or nymph hook does impair the action of the fly given to it by the river currents. When ever possible I will fish with unweighted flies unless the pool or run is so deep or swift that the only way to get close to the bottom is with a weighted fly. I don't fish the GP in great lake steelhead rivers but do large nymph imitations similar to the GP.
I think I have caught more fish with unweighted than weighted flies buts thats just a guess.
My .02 cents on that one.