Hey guys, thanks for the comments!
As I have said earlier, I have tried to remake a real scene I saw up there in a plane. I assure you some of the big clouds had a similar light scattering as here in this render. Not all big clouds are actually very dense. I don't know how often you are actually up there, but as someone who is having this experience about twice a week, I can tell you it's not so unusual as you might think. I might still increase the density in future renders slightly, but only ever so little.
Anyway, I will probably move on from this image to a similar one. I have another one in mind, also with multi layered clouds.
Secondly, I would like to develop the ground a little further. I need to make it look less artificial, somehow.
@Martin, yes, my "bea$t" is a lot of fun! I don't really have a good measure except that old benchmark scene, but in my scenes it feels like it's twice as fast as my old PC. I always said I will only upgrade for at least 2 times the speed, and the new PC is giving me that.
- Frank