I havn't used the Extratour company, but Vait from there managed to supply me a new Mefo Stonemaster for my DR when I was there in September. He gave me some good advise about riding in Mongolia and seems like a top bloke. Actually Rene from the Oasis who is an equally top bloke put me onto Vait.

I rode on and around the south road (or is it the central road?) from UB to Olgi and out that western Russian border, it's amazing scenery as everyone says and I found it easy enough by myself. It's easy to take a few short cuts or long cuts off the main road if you want a bit more adventure. I did this quite often and got lost a fair bit, all part of the fun, just stick to the general direction that you want to go. There are heaps of tracks everywhere, trailriding heaven!

Was advised not to do the North road alone (by Vait) due mainly to the number of river crossings, but then someone else (who had lived in Mongolia for 12 years) later told me there were not that many....conditions do change pretty quick in that country, thats the one thing everyone seems to agree on!

As previously mentioned Rene at the Oasis usually has a few bikes, I met a couple of German fellas heading into Mongolia as I was leaving that were looking to get rid of their XT600's in UB, I told them about the Oasis. That was mid September...might still be there if you sent an email?
Rene has a mate in town with a bike shop too, there was a XR sitting there at that time might be worth a look.
Good luck, wish I was going back....