We own both, the ZPacks Exo and the ZPacks Arc Blast. Both backpacks use the same bag on a different frame. The Exo was the predecessor of the Arc Blast. I'm using it for a couple of years now. Once ZPacks replaced the Exo with Arc Blast, my wife got the Arc Blast. She prefers that design as she loves to have a mesh panel that keeps her back from getting sweaty. My Exo has the 52 l bag and my wifes's Arc Blast has the 60 l bag. Both of us added two hip pockets and two shoulder pouches from ZPacks to our packs. The following list describes how we both pack our packs for the JMT.
Bottom of pack - 13 l drysack with sleeping bag and down jacket.
On top of sleeping bag all the way to right side - Bearikade Expedition
Space next to the bear canister - Sleeping pad (NeoAir xLite), tent (SMD Haven)
Top of Bearikade - 10 l drysack with clothes (long underwear, second socks and underwear, balaclava, gloves)
Left sidepocket of main bag - Caldera Keg-F Stove System (incl. stove, pot, mug, cup, Ti spoon, sparker) + 8 oz fuel bottel
Right sidepocket of main bag - TP/Trowel/Wash kit + Tenkara Pole
Left shoulder pouch - 20 oz bottle
Right shoulder pouch - 20 oz bottle (or camera as one bottle is mostly enough)
Left hip pocket - Camera (Canon Powershot SX 150)
Right hip pocket - SteriPen Freedom, headlamp (Zebra H51), personal first aid kit
Center mesh pocket - rain jacket, rain mittens, maps (in ziplock), ziplock with fishing stuff (flys, lines, tippet), DeLorme inReach
Left shoulder belt - GPS (etrex 30)
Outside/top of backpack - solar panel (PowerFilm USB+AA charger)
The Zpacks Arc Blast with the extra hip and shoulder pockets would save you around 3.5 lbs.
I hope this helps.