Just finished 42mi 3days using the Exo pack and here are a few impressions (averaged 12-13 lb total pack weight, ranging from 15 to 10) :
Compared to the Exos 58 I used before, this pack was better fitting (for me) and the ability to play with the frame length was great. The weight difference is huge obviously. Moreover, I did not miss any of the Osprey features. Size is also very comparable, but the Zpacks Exo sits better/ feels tighter.
The padded belt is great, very easy to transfer weight to hips.
Had no hint of discomfort on shoulders, hips or anywhere else.
Could not feel the frame once the pack was packed.
I do not have the pad holder, but packed an open sleeping bag, with no bear canister there was no pressure on my back.
The material feels very solid, very little bushwhacking on this trip, but not a scratch. Sawing looks impeccable.
I did not feel ventilation was much different than the Exos since I would release the shoulder straps and let the pack lean backwards slightly mostly supported on my waist. This provided excellent ventilation.
The side pockets are wonderfully designed, I am not very flexible and could easily reach both. 2L platy full fits easily.
Load lifters did not do much for me, but did not bother me either.
The added belt pouches are huge, really huge, they were not in my way, but I kept trying to figure out what else I can put there beyond lunch, snacks, phone, sunscreen, mosquito replant, lip balm...
Summary: I think this is as close to a perfect pack I could think of. Every aspect is well designed, super light and feels very solid at the same time. Still have to try it with a bear canister, but given that I could not feel any discomfort on long days, I expect 4-5 more lbs would not be an issue on longer trips (with usually less daily average miles).