Brancher,
I carried the Atmos 50 from Damascus till trails end up on MT K. Yes I did have an issue with the mesh material (both back and waist belt areas). I contacted the Atmos company and they mailed me a new pack while on the trail ( Fort Montgomery post office, NY). I sent the old pack back to them when I switched them out. When I reached the top of MT K, I noticed the frame was broken on the newer pack. Not that I put in too much weight, I put in too much stuff. I called the company again and they sent me a second pack when I returned home (plus I sent the old one back again). This one had a different type of mesh material and though not trail proven yet, it looks and feels much stronger. I am considering taking the 50 on this Spring's PCT attempt, problem is the volume may be too small once again (a water volume and water weight issue through the Desert). The 65 may be what I need so I will look into it. This way I can carry a Bear canister when needed/required. I do have the Osprey Aether 75 as well but, its too big. The 75 is my winter pack (big and able to carry a load).
As far as sweating goes, there is no way to avoid it. The mesh area does help but it still gets a little funky. One evening I had hundreds of one inch black ants move in to the back mesh area, they kept showing up all day long running across my face as I went north. It was hard to get them out of there. Ah the memories.....
What ever you or anyone who reads this post chooses, just make sure you are measured and fitted correctly. For me the Osprey system carries well. Good luck and enjoy. Wilderness Bob