My experiences have been a bit different. Even though I am a small woman, when I was younger (not a grandmother!), I regularly carried 14-15 days food. Even for a big man, food weight can easily be limited to 2 pounds per day (about 30 pounds). The key is to bring the right kind of food. I can get by with 1.3 pounds per day. I think a strong young person can make 15-20 miles a day (with low to moderate elevation gains) on a trail, starting out with 14 days food. You go slower at first, and more miles as you eat up the food.
But I agree that your original plan for 50 pounds of food will get you into that vicious cycle that Brian Lee is talking about.
When I carry a lot of weight I prefer an external frame pack, particularly if you will be on trails and road. Off-trail, less so. This preference of mine is partly due to the fact that internal frame packs in woman's small size are very limited in capacity. Not so much the case if you are a big guy. I still like my old Kelty from the 1970's. I have sewn a new pack bag for it that is much lighter than the original. I grew up on external frame packs, so they do not seem so unwieldy to me. For 9 day trips or less I use an internal frame pack.