Well, that and the pixel filter. I suggest you start with a very simple scene with just a few elements that easily show aliasing (like a box with a very detailed/high contrast texture, a few dynamic hairs) and try out different values for shading rate, pixel samples, post filter type and size. That will give you a feel of how they affect your image and the render time. You can also have a look at how the automatic settings in P6 use shading rate and pixel samples.