Levity 60 at $201 !!! Thats $14 below REIs super sale and REI DOES NOT have the medium size- in fact I was told the Levity is not available in medium by REI employees. Because I wanted to use my member discount I fell for that ploy and ordered a small.
Having tried it with my "normal" over 30lb load I love the Levity but its (painfully)obvious a small is NOT a good fit for someone who fits Ospreys medium packs. There is actually a size overlap by Ospreys specs but a warning: if you are not in the middle or lower end of the fitment spec, the strap padding will not cover your collarbone/front chest and will under deliver the comfort it can.
I'm doing a review of all 3 Airspeed suspended models in the review area here but the short version is I'm old, boney, and flabby along with a skinny frame and its looking like load for load the Levity is going to be the most comfortable between the Stratos, Exos and Levity. I attribute this to the much wider frame used, the small Levity was 4" wider at the bottom then my Stratos medium and that makes the mesh suspension wrap around one's hips significantly more than my Stratos. I tried a 2018 Exos in the store with 35lbs and it felt good but did seem to have the seam/hardspot that can chafe a little in the long run. Along with the wide frame, the Levity has its belt/hip strap spaced out 9" wide (small size pack) vs the Stratos medium at 6.5". I think we all know everyones back is more than 6.5" wide. The effect of this spacing is the Stratos rides further "off" your back/hip ares and has a much smaller contact point with the mesh suspension... while the Levity pulls you further into the mesh and the strap pull is straighter and more effective at keeping the pack on your hips. A side benefit of this design is you have less foam/strap trapping heat and sweat around your hips. The Stratos is supremely good at padding up any and all pressure points but at the cost of covering a lot of your body.
This evening I will also own a new 2017 Exos- I love belt pockets and decided to get one before their are no more available except at rip off prices but have to say the call of the Levity is strong and odds are I will end up owning all 3 Airspeed Ospreys. So if you have questions fire away, I think the whole question of pack choice is SO much more involved than any of the reviews from the normal sources can relate. My take is most reviews of the Levity are damning with faint praise, a bum rap in my view so far.