I ended up purchasing a 35 L, in addition to the 25 L, for dead of winter trips where the 25 was getting a little full (if it gets really cold, I like to carry a down half bag, heavier parka, little more pad, etc). With snowshoes and shovel, my loads are getting close to the 20# mark and I find it carries very well. The frame is removable if you don't need the load carrying capacity.
The waist belt is more substantial than the 25 as well.
