I hate to disagree with you guys - but heavier weights can be packed and are packed for longer hunts. It truly depends on a guy's physical condition, build and desire. I am 5'9" and weigh around 220 (my buddies have compared me to a log/stump). While hunting in wilderness areas of Colorado during the '90s it was common for me to pack in packs weighing 80-90 lbs (including compound bow strapped on back)- 4-6 miles on uphill trails.
Difficult? Yes, but for a 9 day hunt by yourself - it's nice to have some tasty food and some protection from the elements. By the time I come out I have dropped around 20 pounds of food and have room for a boned out buck. One year I packed my camp and buck out 4 miles in one trip - pack weighed in around 125 pounds. Damn near killed me due to the fact I had just packed in that morning 4 a.m., shot my buck midday, boned him, packed to camp and packed out to truck at 10pm. Was pretty satisfying.
Last year I was fortunate enough to shoot a Bighorn ram - unfortunately my daughter had her first gymnastics meet that same night. Needless to say, I was short for time. After packing out the rear half and backstraps on the first load, I decided to go for the front half in the second load. When I say half - I mean ribs forward minus the backstraps - head/horns intact. Talk about a load!!! I have a Cabelas Alaskan II and the left shoulder strap broke at the buckle after I got it on my back. Since I was hunting alone, I decided to finish the load with the one shoulder strap. I know you're thinking it was a small ram - not really, he scores 166. I've got a great set of pictures of what the ram looked like strapped to my pack if someone can show me how to post them.
Notice I said I carried these loads in the 90's - well, I'm getting old enough to understand why you guys keep your packs under 60 pounds. I have been working with a buddy whose into extreme lightweight packing (25lbs for a week)and I'm getting my pack weight down. Learning that it might be easier to be a bit uncomfortable than too tired to do what I'd like for the whole hunt.