Get Your Shading Done First

You do a high res sim and then start shading it and test renders take ages, you can of course lower the illumination resolution in the render settings but I find you get a better feel if you simulate at a low res and get your shading, density thickness, multiple scattering etc set up quickly using a low res and then life is a lot easier with the high res. You could of course cache velocity and upres from there once you have your shading set up