I talked to the Mercedes reps at the Paris arms show Eurosatory in June 2010 about the Zetros. They told me there was at least a possibility one could order a Zetros with a >3:1 low range in the transfer case. Which would be a real advantage over the stock 1.4-1.6:1 found in both MB and MAN big trucks.
Charlie
Not that many of us will have the necessary combination of funding and tolerant government regulators to take advantage of this, but even so, I highly recommend taking the time to look through the pictures and, especially, specification list, to see what's involved in this type of rig and how it can all come together. Very impressive.