I thinkI"m right in between and med and large.. The Med fits pretty well opened up a good amount but feels like I'd probably be able to make either fit. Packed up my Jam today with my WI, burrow, WBTraveler, Gaurdian bug net and ziplock camp kitchen and my 12x14 chinook tarp and I'll definitely have room for a jacket, socks, water and food for 2 or 3 days.. goin back country I'd treat water so that being said it'd probably work on extended trips as well, have used none of the extra space in the collar. Between this and my Golite Trek (which I still have to get) I should be covered for any trip. This is the lightest I have ever been packwise and I gotta say I'm freakin' lovin' it.
I'm not a fan of the foam insert for the back panel. Does anyone know if a Gossamer Gear convoluted torso pad will fit in there instead?