OP, I seem to be in the same dilemma as you. I'm still in the planning phase so no real life experience from me, but I'm a bit neurotic when it comes to planning so I like to think I have a pretty good handle on things. I had an idea for this situation and am curious what users on here think. Here goes nothing.
Basically as OP stated there arent a ton of on/off road options when it comes to 19.5" tires, and pretty much all of them result in a very harsh ride and poor MPG. What I was thinking of doing was buying a set of aftermarket 20" diameter wheels (there aren't a ton for 10 lug, but theyre definitely out there). The 20" diameter obviously has a much bigger selection of tires and there are some that should have no problem holding that weight. The Toyo Open Country AT3 just as an example (which I run on my current SUV) are available in many sizes, but lets take the LT295/65R20. In a single configuration they're rated for 4080 pounds, so effectively the tires on the front axle are good for 8160 pounds. Now on the rear axle, in a dual configuration theyre good for 3750 pounds each, so effectively you have 15,000 pounds worth of tire capacity on the rear axle (thats 23,160 pounds total for those who are counting). I also imagine that the Open Country AT3 will ride significantly better than any commercial tire.
The only downside is that you don't get 6 way interchangeability with an aftermarket wheel setup. I spoke to someone at a company that said an additional inner rear wheel would serve as a great full size spare for the inner rear wheels or the front wheels, so the only issue would be the outer rear wheels. Now you could carry an additional outer rear wheel, or just plan on limping to a service location in the instance of a flat, but either way you get pretty decent piece of mind with just 1 spare.
Again, its all in theory so I'd love to hear some feedback.