Many people have riden that section. I was planing on doing it on my Burgman June last year but skipped it as my Kazakh visa was running out and I was already having problems with my subframe fracturing due to the bad corrugations on other Kazakh roads.
Best route would be to head north from Aqtirau to Oralsky, then west to Aktjubinsk then south through Chromtau. The direct road from Aqtirau to Aktjubinsk is supposedly the worst road in all of Kazakhstan, and unless you are a masochist, is not worth the trouble.
Garry from Oz.
Garry from Oz - powered by Burgman