Selecting a drivetrain for touring bicycle
As other posters already mentioned: Rohloff seems the way to go...Super reliable and sturdy, but: hard to service for yourself "on the road".

On the other hand: if you have a Shimano (most common) 9 or 10 speed Deore XT drivetrain, it will also be hard to find (and thus service) spares in the middle of Africa..:)

If cost is no subject: forget the Surly (albeit a nice platform), and go for a rim-brake Pinion bike.
Why?:
Super reliable, more then enough spread in gears, it enables you to switch wheels (obviously not possible with Rohloff without losing your gears..) and the rim brakes don't make it a pain in the A@% when your wheel is broken and you want to use an alternative..

Maybe not the straight forward answer you were looking for, but if "the Ultimate touring bike" is required this might be the ticket!