If memory serves, normal concrete has an R value of about 1 per foot, whereas AAC is more like 1 to 2 per inch. So, an 8 inch wall would have an R-value of about 8-16. That doesn't seem like enough for a cold climate, so I'd assume for those applications you'd probably add an extra layer of actual insulation. (This would mean having pretty thick walls.) You wouldn't need as much supplemental insulation as you would with a regular concrete wall, though.
The thermal mass is also nice, though it doesn't really help much in winter-time. I think AAC is a bit more suited to warm desert climates where you have a daily hot/cold cycle.
20-inch wall is enough for pretty cold climate according to my calculations. Either that or thin wall with insulation (or thin wall and more money on heating which might be an acceptable solution, if you have cheap coal and your country does not care what you build).
Yeah, that sounds right. Still, a lot less than concrete can still be a lot. And I think in most cases I'd rather have better insulation than more thermal mass.
The thermal mass is also nice, though it doesn't really help much in winter-time. I think AAC is a bit more suited to warm desert climates where you have a daily hot/cold cycle.