Having owned a couple of Ospreys, I noticed no difference. The connecting points of lumbar and shoulders leaves a gap for ait floe. Besides, the way I sweat, no "air flow" design on a pack makes any noyiceable difference; when tramping, I am always drenched in sweat.
Glad you enjoy the Lightning as much as I do. It's my favourite pack by far. I actually took all the little compression ribbon off mine. I doesn't need it. It's such a simple pack with an amazing harness.
I like the ribbon/webbing on the pack. And that the lose straps neatly velcro to themselves. I HATE straps flapping around everywhere! I'll say it again; greatest pack - by far! - that I have ever owned.
I had a lovely pack for 65L which served me for years, but I always wanted to have a bigger one because I couldn't pack my mat in and had to tie it. Finally I've got the one for 80L but I just love my old one .
I have an Osprey, Macpac Traverse, Aarn Effortless Rythm, Aarn Natural Exhilaration. Each has it's uses. However The Aarns are the most comfortable I have ever used.
Plus since being fitted with a pacemaker the Aarns do not place any pressure on the area where it is located which is a big plus for me. The others are a matter of careful adjustment every so often to ensure they don't rest too long in one place.
Interesting about the pacemakers. I might try to remember to pass that one onto the pacing technicians to tell the patients. Aarn packs are also good when you're scantily dressed above the waist (or not dressed) for a bit more modesty. Aarn hadn't of heard that one when I told him!
Just checking out 40L packs when I came across this !
Black Diamond Saga 40 JetForce Avalanche Airbag Pack