Regarding overpacking, let me relate an experience from an extended backpacking trip while in college. We were hiking the entire Long Trail in Vermont. During the first leg of the hike, my backpack frame actually cracked probably from being overloaded. I took that as a sign. We went through all of our gear and removed everything we didn't absolutely need. I mailed it all home in a big box. The trip was much more enjoyable with a lighter pack. One of the things I mailed home was my down sleeping bag, which I replaced with a space blanket. That was fine for the first 3-4 weeks, but I got very cold after for a few nights after a cold front came through. Ended up hiking into a town to buy a woolen blanket to carry the remainder of the trip.