I just took my Crosscheck out for its first real, even if it was short, trip and it worked great for me with just two small Ortliebs up front, a small frame pack, a handlebar bag, and the rest of the stuff strapped directly to the frame. We only did 5 days out but aside from adding some cool weather clothes and a sleeping bag (4+ lbs), and a couple more tools and a spare (2+ lbs) I'd say the rig is totally cross country capable.
Bike and all was about 70lbs fully loaded for an unsupported urban to back-country style trip with 3 days worth of food and over 2 1/2 L of water. I don't know how well it would do with a bigger load but I wouldn't want to carry more anyways. The bike did great on paved roads, graded limestone, fireroads, and a bit of overgrown muddy FL singletrtack. The steering was a little slow but the bike felt super stable and the the load was not very noticeable.
I might have bought a Straggler if it was available when I ordered my CC. The slightly more relaxed geo will be a plus, the disc brakes will be a wash, and the only downside I can see is that I've read that it can be tougher to mount fenders and racks on the bad beast but I bet that can be managed.
EDIT: The complete build CC is easier to convert to a triple than the Straggler. I'd also price out a piecemeal build with bar end shifters or Gevenalle/Retroshift levers.