Jeez, I have the Atmos 35 and it's a challenge to stuff an overnight kit into it with any kind of normal bag and clothing, as well as the usual lumpy gear and a water bladder. OTOH it's a great winter day pack, or anytime I'm lugging camera gear. The trampoline back panel is terrfic at keeping hard corners well away from my back and is very cool in summer.
The main compartment shape--narrow and shallow on top, wide and deep on the bottom, doesn't lend itself to easy overpacking like a more traditional top-loader. I know I wouldn't be able to use the 25 overnight, but YMMV. Have you looked at the Talon series?
Has anyone used this pack for overnights??? at 1500 cu3 i thought it to be a little small but i seem to be able to fit my hex 3 my pot/stove combo/ food for a few nights and my rei flash kilo in there with some room to spare...if anything this could be a strictly summer setup i was thinking... Does anyone have any experience with these bags?