If you already have a functioning pack, keep in mind that there is an outfitter directly on trail at Neels gap, 30ish miles from Springer mtn which carries a good variety of ultralight backpacks and will have more packs geared towards thru hiking than an REI will have. It is where I bought my ULA pack and got my wife her frameless Granite Gear. If you are so inclined, you could easily use your current pack for the first few days and then buy a lighter pack once you get to their store.