I understand what you are saying about creating smaller groupings of clouds and then compositing them together, offsetting each of their timings. Unfortunately, I don’t know that that will work in this case as the cloud has to maintain a relatively specific shape. But it is definitely worth thinking about.
Here is a simplified project file that I have been experimenting with. The movement of the cloud is actually going to be tracked to a live action shot (and so will have a ton of keyframes – this experiment only has three…). You can see I was able to add a formula effector which rotates and pulsates the particles individually, I just can’t seem to be able to offset their timing as far as position goes.
12443_cloudtest01.c4d.zip
Thanks!
Sandy