I've always gone by the 1/4 of your body weight also, but in reality you do have go with what your body wants and doesn't. As you get older things change and the back and muscle can't handle the same strain. I'm not there yet, but I look into the future another 20 years and know I probably will be. It's very important to stay in shape. I try to and my work has a good amount of physical activity to it besides. My current pack is about 50 lbs loaded and my rifle and magazine pouch make another 20. I'm 250lbs and thankfully low on body fat and still a fair amount of muscle so it still works. My BOB is abased off a long term sustainability outlook and gear though, not a simple 3 day. If shtf and I need to resort to my BOB rig, it's not going to be a 3 day problem. I can stay home or in a hotel for minor crap like that. I've been through enough stuff that make other people cry and pout like little bitches. I know because I've seen it enough. So, if I need to resort to bugging out on foot and surviving with my BOB, the world or my world, has seriously fallen apart.