O K, here goes. Tried your setup with some tweaks @ 1280x720 and after 6 hours and almost 1/2 way through spotted artifacts so cancelled out and went back to my normal method of tiny tests. TestSky04 was my preference so I rendered it at 900x506 but all are in the 'test strip'
In the attached .tgd you will find .tgc's of all the skies with only 04 connected. Simple enough to preview any of them that way.