I currently use the older model Gossamer Gear Gorilla which has some wicking mesh on the back, but it rides right against my back. With temps in the 50's F, my shirt isn't very wet from sweat anywhere except the back. My back is completely soaked as if it were 100 degrees out, and the sweat even starts to soak the back of my pants after a few hours. Except for this minor issue, the pack is great.

Some Osprey packs have the ventilated mesh back which is not in direct contact with the wearer's back. I think the extra half pound of something like an Osprey Exos 40-ish liter pack would be worth having a drier back as long as the pack is as comfortable as the Gorilla. I rarely carry more than 15 pounds total weight (including food and water).

Has anyone tried both an Osprey with the vented back and the Gorilla? Or tried the Osprey and packs with a minimal frame similar to the Gorilla? Any Osprey users want to comment on the comfort of their pack?