Ther eare many, amny ways to optimize such things! If you're using volumetrics, try rendering a particular material on a blank sphere in a blank scene, and get a feel for what level of "Quality" slider you need. For skies, well, if you can optimize volumes skeis are a piece of cake. But the real optimizing come in on the lighting. Are you using LOTS of lights? Are any of the set to negative? Are they all at linear falloff, or are some at squared? Coudl a light array, in a certain situation, be replaced by Bryce 5's softshadows? You already know all this, Gog, I only post it for reference...