I've ridden/ owned the 1200GS, tiger 800xc, and nc700x on adventuring trips.
For sizing the bike, critical factors would be:
- how much highway riding (70+mph) do you want to do (hours/day) and for how many days of the trip?
- how much broken surface riding do you want to do each day?
- fireroads/country roads
- technical two-track / jeep trails
- very technical single track (dirt bike territory)
There's a continuum as you get more technical offroad to need better breakover angles and ground clearance, which will raise the center of gravity and have the bike be more topheavy--its just physics.
That said, physics is also what keeps the bike up in proper adv riding, not waddling, and pretty much all marketed adv bikes will be rider limited... That goes both ways in the sense that if you oversize your plans and ambitions, you may also struggle through the bike until you master it offroad, which can be a costly learning exercise that most will opt out of (sensibly so.)
Good buffeting mitigation and horsepower help with long highway hauls. These tend to be best featured on the 1200's.
Rims that let you run tubeless tires ought be valued highly - changing a tube on the road is no fun, but a plug is quick.
Highway pegs should not be underrated for long hours on slab.
I wouldn't use an adventure trip to deliberately test the boundaries of your offroading or sport riding capabilities. Realistically, it will grow some slowly through unintended, marginal exposure. Ideally, you try and train locally.
For myself, if I had the dispensable funds, I would go back to the GS because I already can ride it everywhere I intend to go (technical double track at worst.) But I have kept the Tiger 800xc, and I know I can do just as much offroad. I love the nc700x for its fuel economy and as a commuter, but my iron butt is only case-hardened, and I wouldn't be willing to take that on high speed highway for days on end, nor would it be wise for technical two-track--low ground clearance as the only reason. The downside for the tiger is that while it is good on hp, its only OK on buffeting mitigation; after a few days that entail 6h of high speed slab, I am wrung out.