TG4 / Upgraded Airship models / xFrag trees.
Small Render 1280x720 pixels using OOTB parameters:
Render time 5 minutes 27 seconds
Not Bad at all. With the fog (Actually Easy Cloud Alto-cumulus ) would have estimate this to more of 10-12 minute render.
Large Render 1920x1080 pixels (detail .4, AA 4, GI Cache 4, GI Sample quality 4)
Render time 23M 48 Seconds