If you can wait two weeks, you may use Terragen2:
“Terragen 2 Technology Preview will be the first public release of Planetside Software’s new, cutting edge landscape visualisation software. The Technology Preview will be made available December 15th, 2006 for both Windows and Mac OS X 10.4.x.”
If you can’t wait, use some layers of massive cloud-images in the background and put plenty of messiah clouds in front of them, you will get very long render times but I guess it’s your best and only choice(In Messiah). I think your fancier test looks quite good but it’s not massive, so you just need to add MORE and MORE clouds and accept long render times! And you can always use Terragen1 to generate some cloudyskies for the background ; )
/ Svante





