Having juys ridden my XT660Z from UK to Mongolia through the countries you mention I can state with experience that the majority of fuel stations will be able to supply 92 RON or above. There are only a few in Mongolia where we had to be happy with 80 RON but if you carry a bit of extra fuel in a can you can avoid that and go to the next fuel stop.

We did the Southern route across Mongolia so it may be a different story if doing the Northern route.

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2011 XT660Z, in BLACK of course!
Mods done:
Lost the will to keep track!