In 2013 the road from Astrakhan to Atyrau was very poor asphalt, long streches of potholes. From Atyrau to Uralsk the road was excellent, freshly paved.

In 2014 we crossed Kazakhstan from southeast to the north. Main roads are generally acceptable. You will find parts not worse than any European road, and parts that are quite bad. Occasional sections of roadworks might put you on unpaved bit for a while, but I see no need for TKCs. We did it 2-up on a road bike with 120/180 road tires. If you wish to see places like Charyn Canyon (which I would reccomend) than you will have to take a few dozens of unpaved kms.

However, I would not ride in those countries on 75% used tires, as the most common question from local folks regarding the bike was how would I fix a flat tire.

We did not go the way you're planning, but from what I heard from other travellers, last summer there was a stretch of 150-200 kms of roadworks south of Baykonur which was tricky when wet, but I suppose that it might have been finished during the last twelve months.

Shymkent-Taraz-Almaty-Chinese border was (quite) good. Almaty-Astana good to so-so. From Astana towards Kokshetau there is a proper highway for 200 kms, than 150 kms of very good road which ended abruptly 100 kms before Petropavlovsk. The road from Almaty to Troitsk in Russia is good. For Kazakhstan standards ;-)