China's just too big to describe a plan in terms of mere weeks. A month-by-month account of where I might be:

Month 1
Crossing over from Kazakhstan, taking the best part of two weeks to get to relative civilization in the form of Urumqui... despite being the farthest city in the world from the ocean. I'm hoping that this route - north of the Tian Shan mountain range - will be cooler than the other side, the Taklamakan desert.
  It won't last though - moving onto Turpan, the hottest place in China ("searingly hot" actually), I'll then spend a couple weeks crossing the Gobi desert (!) before, at long long last, reaching salvation - Jiayuguan, the westernmost outpost of the Great Wall.  Hopefully, I won't have run into any marauding barbarians up to this point.

Month 2
Winding my way down the Hexi Corridor, there isn't going to be a great deal of diversion until Lanzhou. Originally a major caravan stop, and the sight of a statue of Monkey and Tripitaka (remember them from BBC2 ?), who also passed this way. Onto Pingliang, tucked away in the foothills of Liupan Shan and then onto Xi'an.
  Of course I'll take in the Army of Terracotta Warriors as well as the other major sights, but also hope to spend a good few more days resting up and taking in the atmosphere.  Only a month to Japan!

Month 3
Song Shan, the central mountain of Taoism and also home of Shaolin kung-fu, then a long ride to Nanjing, with an abundance of historic sights in and around.
  Then, via Suzhou and Shouzhuang, I'll finally arrive, hopefully, at Shanghai.  And a holiday, a real holiday at last!