I'm going with the 5-ton MV, because it's robust enough to deal with the majority of the roads I'll be on, big enough to house a decent sized living space, and I can make it very modular, very easily for future shipping to Africa or Russia, my next destination.
I will spend about a year out in the desert in AZ, torture testing the vehicle before I go for my trip. This should give me enough time to really learn the limits of the platform. I will also be putting 2-250cc dirt bikes in the back, and plan to use the 5-ton as a base camp. This is why I don't need a smaller platform. If I want to see some awesome sites, I can basically just plan my route with a 100 mile radius around the road, so if I want to go explore, I simply park the truck and unload the bikes.
I just simply think this is the best platform for all the things I want to do. I also am thinking of worst case scenarios in a 3rd world setting. What happens if the road is obstructed because a semi truck is broke down, and I could tow it to a wider spot, to get by? An 8x8 would just be too much, and like I said, fuel mileage is somewhat important.
With and ISX cummins and the right trans, 7mpg is a good figure to hope for. Also I need the whole right side from fender to engine, to use as an enclosed "tunnel" to access the cab from the camper, so a MK-48 won't work. And all the 4x4 options are just too small for all the things I want. Again, I plan on being on this trip for a year minimum, living out of this truck.