>>2408176I don't have anything but anecdote, so take with a grain of salt.
I switched from 10+ years framed to internal frame about four years ago, when I started getting serious about lightweight/ultralight backpacking. In my opinion, the frame only helps when you are carrying above about 35 lbs continuously. Otherwise, a frameless or internal frame pack is superior. The only time I carry a frame now is when I'm hunting and anticipate carrying out a deer.
In my experience, the frameless / internal frame holds weight just fine until it's heavy enough the pack will not distribute the weight correctly. Then you'll get uneven weights in your shoulder straps or rubbing on your hip strap. Once this happens, an external frame picks up the load and properly distributes it on your shoulders and hips. However, the trade off is the external frame adds weight, and it generally shifts the weight away from your body, which makes it feel like something is pulling you back constantly. As you might imagine, this is much more uncomfortable for anything of substantial distance.
Internal frames generally have load distributing straps that try to keep weight as close to your body as possible, which makes the weight feel like part of you, as opposed to something strapped onto your back.
