I've never fished a class A rainbow stream in PA. With that being said there is a river system in SW NY that is full of wild rainbows. It's a lot like brook trout fishing. The fish are relatively small, there are lots of them, and they hit almost anything. In this river system, the rainbows only live 3-4 years so they rarely get above 12 inches. I'd assume PA class A rainbow streams would be similar, but I'm sure someone will correct me if I'm wrong. In other words, if you are after a lot of smaller bows, try a freestone class A stream. If you are after a large bow, try a class A spring creek (Big Spring).