Thanks Ben2world.
I had been toying with the idea of buying one of each and I'm glad someone with more experience thinks it makes sense.
I need packs for myself and my wife. We plan an AT thru. While we're looking and learning, we've been using ALICE packs that I have been modifying as we go. I removed the external pockets from a medium and fitted it with a large pouch on the front that is waterproof material on one side and expandable mesh on the other. (Goes on and off with Velcro and some light rope.) We experimented with carrying our Tarptent Double Rainbow in it. The idea was to mimic the Catalyst, in that a big mesh pocket makes sense for carrying a wet tent or tarp, which seems like a good bet on an AT thru.
I've been day dreaming that the Catalyst would work well for my wife, Mudpie, and the Nimbus Merdian for me. I like the idea of a removable lid that doubles as a fanny pack and I like lots of pockets and webbing. I understand GG makes add-on exterior pouches.
What I really want to know is if these hold up for entire thru hikes. I've heard GG's tend to bust seams after several ghundred miles, which would not jive with Trauma's 10,000 mile experience with the NM.
Thanks again.