Have you tried out the Vray Sun and Vray Sky? Here is every setting explained using images. Basically, this guy has tried out all the different settings and posted his results. This is a good way to find all the optimum settings for your project without having to do all the testing yourself. The results can be very pleasing if you get your settings just right, so this is definitely worth checking out. Could save you tons of time. Remember to click the tags and explore more helpful posts.