I prefer the DX40 to the lighter weight x-pac fabric, it gets dirty easily but seems extremely durable and I really don't care if it looks dirty. I did a fair amount of bushwacking on the trip and see no signs of wear. The vx07 is too light for my uses, the vx21 is borderline. I spent a lot of time fishing my way up a creek, both in the creek and along it's banks through the brush, all the while wearing the pack because I didn't want to have to go back and get my gear. This is the reason for the removable pocket and lack of side pockets, when the removable back pocket gets trashed I can make another, or if I don't need it for a trip I don't have to bring it.
I really like the versatility of being able to add and remove straps or a pocket depending on my uses. I agree it is a very underutilized method.
BTW I love my tenkara yamame rod.
I am using a 3/8 evazote foam for the shoulder straps.
I wish I could make it on the october trip, I am trying to get a day and a half off to do a turbo overnight to come in and join everyone for an evening.