Biggest PA trout - 32 inch steelhead, Elk Creek. Glo-bug, white with orange dot.
Biggest non-great lakes fish - 28" rainbow. Henry's Fork Idaho - night crawler (lol, thats embarrassing)
Biggest non-great lakes PA trout - 23" palomino, Tionesta Creek, PA. Live minnow.
Biggest PA non-great lakes wild trout - 21" brown, Spring Creek, Centre County. Black Sculpin in high muddy conditions.
No doubt you can catch big fish on small flies. But if you're a big fish hunter and want to do it regularly (I'm not), then big flies are indeed the way to go. Fish streamers and such in high, somewhat muddy conditions, or at night.