thanks for the follow-up info to the July query.
as i stated, i'm not sure if the size Large (maybe it was on the G6 packing slip - i'll have to look at the G6 pack closely again), referred to the internal volume or the shoulder strap length. it definitely refers to the shoulders strap length in the G5.
agree with you that the G5 with an SUL base pack wt can hold a lot of food and is a real possibility for a relatively long no-resupply trek and not break (go above) 20lb. starting total pack wt.
my XL gear list showed me that with an UL ~7.5lb base pack wt + 5days food (another 7.5lb) + water bottles full i would only be at ~19.5lb total pack wt, depending upon how much water i want to carry. drop the base pack wt. down to 5lb and thats another ~1.67days of food (all food at 1.5lb per day). increase food by 1/3 more day and take the 19.5lb total pack wt. up to 20lb even. now we're up to (let's see if i have enough fingers for counting this one)...7 days of food if i've added correctly. reduce the water a bit if it can be done safely (i always figure at least 2L of water max carried & so always used the full amount in calculating total pack wt) and add in maybe another 1/2 day or more - now we're up to 7.5days of food without breaking 20lb. total pack wt. i've noticed some people only carry 1L max, so they would be able to get close to 9days of food (at 1.5lb per day) into the pack. of course, i'm forgetting here about adding in 4more oz of fuel for the difference between the 5days we started with and the 9days we ended up with. of course, some GORP only days would loose part or all of the final 9oz of fuel. in my case, with my SUL kit/gear, i don't think volume will be an issue as i use only about 1/2 or less of each side pocket volume and around half, or just a tad more of the front pocket volume. of course, in your case, if you used a diff. pad & put it in the pad pocket, you could fit even more food inside the pack, but then a day's worth of food weighs a lot more (2 times as much???) than the pad, so maybe that would push you over the 20lb mark.
also, i'm thinking that to keep the load inside from shifting as the food is consumed, some form of compression is really helpful if the shifting is objectionable. this could be accomplished with either bungee+toggle or half-inch wide webbing with buckle.
so,...was this what you had in mind, i.e. 7.5 to 9 days no-resupply? any suggestions?