Personally, I rarely throw anything other than a 7wt in this area, but for the brook trout streams, I'll throw a 7'6" 3wt. I use the 3wt on the Gunpowder too. If you're hitting somewhere like Mossy where you'll have a chance at hooking into something bigger, you'll probably feel undergunned with a 3wt though.
The biggest thing to remember about selecting a rod weight is that, within reason, you want to size it for conditions and the fly rather than the fish. If you're used to conventional tackle, think about the bass anglers that have their very light set ups all the way to the big boom sticks for throwing heavy lures into heavy cover. Of course throwing a rod that's significantly undersized for the size of the fish can prolong the fight and risk the fish's health if you don't know how to properly use your rod to fight a fish. If you think you're going to be throwing lots of heavy flies for smallies/largemouths or in windy conditions, it'll make your life easier to throw an 8wt. For the smaller rod, if you're only going to be hitting brook trout streams, you're fine with anything from really a 1 to a 4wt. If you're going to be fishing trout anywhere in the region with weighted streamers with consistency - particularly if there's big fish - you'll want the 4 or 5 weight. Heck, if I go to Mossy in high water conditions where I'm throwing big flies, I'll toss a 6wt.