Hi Chris. All I have read on the internet, even the Thorn tree forum (very good like you say) over the last few years have said that it's very difficult to cross from India to China. (I have a friend in Katmandu who is keeping her ears open for any travellers crossing the border successfully) Even if you do cross the border, you are not allowed in Tibet without a guide, and 4x4 backup, which costs an absolute bomb. Which is a shame because the road is supposed to be amazing (This guy is the Don of cycling Tibet
http://www3.utsidan.se/corax-e/ ).
I am going to fly from Nepal to Bangkok I think, or maybe hop on a train down to port in India to try and get on a ferry going to Thailand or Malaysia, a lot more faff but trying to fly as little as possible. I will cycle up SE Asia to China to get a job somewhere, as opposed to going South like you.
With regards to Iran and Pakistan I think they are going to be pretty sketchy and hard to get visas for at the momen;, I'm sure most of the people are nice, it's more the authorities and the risk of being held kidnapped and held to ransom by some bad egg. You are right though you can go through Azerbaijan over the Caspian sea to the 'Stans, I will be doing this on my return route from China. The 'Stans look amazing, especially Kyrgystan and Tajikistan, should be one of the highlights I expect. Here are a couple of good websites of people who have cycled in the 'Stans (
http://www.timbarnes.ndo.co.uk/tajikistan.htm http://www.cyclingnomads.org/ben/category/tajikistan/ )
However if you take that route on the way you end up with the option of going in Afghanistan or China. If you do cross into China then there is no way to get to India. Damn politics!
I might be wrong on some of this information, but it's what I seem to have concluded after pottering around the internet, I was planning on maybe heading to the States after Eurasia, but seeing as I'm flying over Iran and Pakistan though I would make it a round trip. It means I can take another few years doing the Americas properly in the future too.
I'm heading off at the end of August. What about you? What millage are you planning for by the way?