I've done a good amount of packing. Having been a packer for the Stoney River Lodge in unit 19 and 17 . A couple guides from there had a company Frontier Gear of Alaska. They made an external frame Alaskan Guide pack that later became the Barney's Sports Chalet Guide pack.
The heaviest load I have hauled with it are 2 front quarters from a trophy bull moose. Pack did fine. I did OK.
80 pounds is OK to pack all day. When u get up to the 200 pound range it starts to feel like your spine is going to shear out thru your butt.
There are a lot of guys that can out pack me. But I got er done. The most I've walked in a day packing is close to 30 miles. Half loaded half on the go back. And have done runway sprints with 120+ pounds on. But I beat the other guy to the meat pole
Course I was younger then, hadn't gotten hurt as much. But I can still pack half a caribou or a trophy bull moose ham with the bone in. Used to do a ham and a back strap or half neck.