I adjust the supersample slider in the preview imager node, and I don't see a real difference, but there seems to be a bug with it.
anything over 4 seems to render at the same speed as 1.
Unless it's randomly somehow harder to calculate values between 1 and 4 than it is between 4 and 8, I think this is a bug.
if you want to suck up a lot of video memory, crank this thing up and you will see some seriously higher usage too btw
