Thanks for your comments!
Greg, the stay is 6" at the top and flexes to 10" at the bottom. With the 25" length it could probably stretch to 12" at the bottom.
The total volume is about 3,000 ci. 2,300 for the main pack, 300 ci for the side pockets and between 200 - 400 ci for the rear pockets.
David, I didn't realize the 210d was a midweight fabric until after sliding down a granite wall while wearing it. The were a few cuts and holes in the bottom.
Andrew, I've had the same experience with sewn seams on stuff sacks made with the lighter 0.50 cuben. After two years they start to disintegrate. The backpacks have held up much better, although I usually end up making a new one each year to try a new design. For this pack the seams are sewn and taped. Reinforcing the pivotal attachment areas with 3 layers at 45 degree angles also helps.
I'm going to try a modular design next with the ability to easily use various combinations of shoulder straps and hip belts on the same pack body. UL, SUL or daypack all in one.
Maybe a snowshoe trip into the Ionian Basin would round out your monthly Sierra goal this winter? These guys did the (other) Sierra High Route on snowshoes: