I bought these intending to wear them with a full pack, but haven't done that yet. I do wear a 40-lb weightvest two miles to work several days a week and they are holding that fine. My only real complaint is that my heel is loose, and I get some toe-crunch. I'm hoping that I can solve that by adding another hole up near the top, but a little toward my ankle. Will see.
I also tried the later model, the 103. Did not like that as much as this one.