Have been doodling a bit with a setup I used before, but now adjusted it to have the cloud be taller and it's also much simpler now for me to iterate between tower-shapes.
5000m depth, edge sharpness 2.1 and density 0.7.
Rendered at AA4(max), 150M voxels (Yes Matt, I know..., but it brings out the fine scatter details in the small billows) and GI cloud quality @ high.
Took about 9 hours on my 2600K.
[attachimg=1]