The volume of the Jumbo is substantially more than the Proteus, probably 2 -3 times more (I'll try to get specific measurements for you). However, the setup is different. The Jumbo, as you know, is set up like a backpack. The cargo volume is in deep pockets, so that items are stacked on each other, and under the flap. The Proteus has two wide, more shallow pockets, and two side zip pockets, similar to the one on the Jumbo. As I mentioned in my original post, each have a different situational use. If you're stationary, or traveling in a vehicle, the Jumbo wins hands down for capacity and ease of use. However, if you are on the move, the Jumbo does not move well with you. We snowshoed extensively, and the Jumbo was flopping back and forth on me. Even on steep uphill grades, it slid forward, seemingly against gravity.

One of my thoughts from now on may be to Malice the Proteus to the bottom of the Jumbo for travel, and then, hopefully having segregated my gear accordingly, split off the Proteus as a waist pack for specific use.