Your scenario calls for 40 days out; starting with a 90 pound pack and a "survival" mode for the last 10 days.

I think you are being too pessimistic. Say you go UL and have a base weight of 15 pounds. I can pack a nutritinally balanced 2,600 calories per day in 1.5 pounds. That makes 60 pounds food. Now you have a 75 pound pack. I can pack 3,000 calories in 1.5 pounds per day if I go way heavy on fats, nuts, cheese, etc.

I personally regularly go on a nutrionally balanced 2,200 calories per day and 1.2 pounds per day. You could nudge this up to 2,500+ calories with more fat. This pack would be 63 pounds.

If you do not cook, no gas is needed. If you cooked one meal a day, built some fires when you could, I can see taking 3 large cannisters of gas or about 5 pounds. This would be an 80-pound pack at 1.5# food per day or 68 pounds at 1.2 pounds per day. Still heavy but better than 90 pounds.

I admit confining food to the lowest weights would result in boring meals and a VERY high fat diet. But this is still far from 40 days on trail bars alone!

The stragegy of eating a lot at first to reduce weight and starving at the end does not seem like a very good (or safe) plan. My body works a lot better over the long term on a steady diet, albeit reduced calories, rather than a variable caloric intake. However I think it is OK to go without food the last 2 days.

Were I to plan on being out 40 days, I would bite the bullet and pay a horsepacker to bring in a re-supply and break this into two 20-day rations.