Hi, Knight. You should distinguish two parts in that way we are talking about.
From Aktau (port at the Caspian Sea) to Beyneu the road is very bad, as I said. From Beyneu (still Kazakhstan) to Kungrad (Uzbekistan) the road is more or less half good dirt road and half asphalt, as Colebatch said.
So, If you take ferry from Baku (acerbaijan) to Aktau, you should ride a very bad road, but of course ridable (I think that kind of roads is what we are looking for in the Stans), but if you go from Astrakhan (Russia) to Atyrau (Kaz) you will not ride the worst part, and arrive Beyneu on asphalt (I didn´t ride that way so I couldn´t say how it is).
I did both worst parts: Atyrau to Aral (hell 1), then I went to Almaty and going back by Tashkent, Samarcand, Bukhara, Nukus, Kungrad, Beyneu and Aktau (hell 2). So I ate the Aral shit twice, but I really enjoyed it. My bike is a GS 1200 and everything Ok, so yours, much lighter, shouldn´t have any problem.
Check the blog about that part in my blog.
Blog de Miquel Silvestre
Have fun on hell.