I have one of the prototype Hornet packs, which were 42 L., not 46 L. The width and depth seem about the same as the 46 L. production model, but mine is a few inches shorter. My large Bear Vault will only fit in vertically, which takes up a lot of space. The smaller model BV will fit in sideways, which allows decent room for the rest of your gear (but not a lot).
I did several mods to my Hornet, trying to get it to have a decent carry for 20#. Nothing really worked, and it's been demoted to be used only as a day pack. If you are thinking about the Hornet, be sure to load it up in the store and walk around for 1/2 hour. For me (and many other testers), the torso length didn't work at all, and the thin padding of the shoulder straps and hip belts were a joke. It's pretty light though.