We see a lot of models with high mileage, but as it takes time to add mileage, these are mostly older models. Newer models that are available in todays bikes don't yet have high mileages.Do you remember what were the main models of motor with such mileage ?
Personally, if I were going around the world and carrying a lot of weight, I would probably choose an old Bosch Gen 2 motor. Basically, it's built like a tractor gearbox inside, parts are plentiful, a service kit is available and it's generally bullet proof if you keep the water out of it.