Ok, here is my last argument for 26" and then I'm out.

On a tour that long you are almost definitely going to wear through a set of rims. Almost every tour journal out there that goes for more than a year has people cracking rims eventually. They only last so long. What are you going to do when that happens? Also without a doubt you will wear through your first set of tires, if not your second and third.

Mail ordering a bike rim in the middle of Ecuador is a lot different than doing it in the states. You could be waiting for weeks and paying huge import fees.

Lastly I've ridden identical LHT builds with 700c and 26" wheels. They both ride great, and the 26" bike didn't feel at all slower.

If you are dead set on doing this definitely plan to replace your rims before you leave the states, they'll be near the end of their life anyway.

Good luck.