One more thing, for anyone wanting to try this as well:
The light direction plays a key role in deciding whether this looks great or mediocre.
On the same shot, before this last render, I had the sunlight coming more from behind the camera. The cloud did look quite nice, but not really great. It seemed to be a rather flat wall. Changing the light direction so that shadows could underline the depth of the formation much clearer really did the trick.
Regards;
Frank