Definitely best work so far Henry!
Besides the clouds you also have a nice terrain and populations.
I use almost the exact same technique for setting up my populations and breakup, it works very well for trees indeed.
For grasses I barely use breakup, only slope/height restrictions.
Anyhow, I think this render could be even nicer when you would have more white-ish clouds and with less coverage of the sky to get more direct lighting.
If you ever intend to do these type of images again, and you will! lol , then use the new raytrace function for objects together with at least AA6. AA8 even better.
In case you don't know, the quality of raytraced objects is determined by the AA-setting. The higher the better, but you'll soon find out that AA6 gives very nice results and AA8 probably most bang for buck.
Speaking about bang for buck: to get rid of odd lighting conditions on your objects in shadow areas you might try rendering this with GI 2/4.
Keep up the improvements and good work

Cheers,
Martin