The Audley Trip above and Wild Frontiers below
Audley offered a section by train in China, a road section from Kashgar-Bishkek, then Khiva-Bukhara-Samarkand-Tashkent by road. It would have coered a bit more of China, and the air legs (4 of them) would have cut out much of the long distance drives - though the Khiva to Bukhara leg is still there by road.
On balance, I think we made the right choice to do the whole trip by land (and by horse) and had a better understanding of what the Silk Route was about than we would have done on the Audley trip