I will say the 140 hour renders are very complex with multiple planetary objects, 4 or 5 modified clouds layers, and 5 or 6 populations (very thinned out). Detailed lighting, mostly turned off for the area. Or just usual renders with more detail. When it works perfectly, rendering in under 3 hours at 3840x2160, I touch nothing in the settings... just add more hard disk swap space to 1,350kb. (Somewhere fter about 1,500kb it hurts instead of helps.) Then I use one cloud layer and 4 or 5 populations, at high density... in one area. And adjust as needed. With multiple added elements... including water, but nothing too big.