The Unimog's are real beasts. I had the opportunity to drive one of these things a year or two ago, and was in general very impressed. But its a huge truck, not at all a city vehicle. The gelandewagen is for families, while the Unimog is for real work. I would be surprised to see any kind of comparision between the two vehicles, they are totally different. It could get up to about 60mph, but was pretty noisy. I would guess it could tow something quite easily.
The fellow whose Unimog that I drove lives here in Northern California, and he always seems to have a few for sale. He buys them from Europe and brings them in almost always with low miles. I understand many of which were used by fire departments. I forget his name but you can find him on the net or in the alt.mercedes newsgroups. He could be considered as the U.S. expert in Unimogs and has all kinds of manuals and documents pertaining to such.