Virtika has a Style and Fit guide that shows how different sizes fit on different people. Choose the model that is closest to your height and weight and then you can select a variety of sizes to see how they fit. Also check the size chart and compare it to some gear you already own. Keep in mind that sizing changed a few years ago so the newer gear will fit differently than the V3/V4 pants.
http://virtika.com/style-fit-guide/