Thanks :-)

The clouds took about 12-14 hours (so about half the time) with Godrays turned on and a quality boost of 0. I used Dave Burdick's tip and increased the object anti aliasing quality to 95 % to get rid of any noise. I already knew from past experiences that inceasing the Quality treshold increases the rendertime for several oders of magnitude, especially for very fine details like grass, but nontheless 20 hours with a Core i7 @ 3.6 Ghz for that bit of dynamic population is still too long in my opinion. Generally I find Vue 8 to render much slower than Vue 7, independent of the scene I load. All my old scenes, no matter if they have clouds or not, take about 1/3 more time compared to Vue 7 with the same custom render settings applied (and not the changed render presets in V8, I know their quality was increased so they take longer now). I hope this gets better with future updates.

And both the new displacement methods and the terrain editor are so far pretty much unusable for fine details, at least the software keeps crashing frequently on my PC due to very high demand of memory.