Is anyone setting their difficulty? I see that you can do it on suprnova pool by setting d=(difficulty) but is there any use in doing this?
It depends on the speed of your rig. If you have a slow rig, you want low difficulty to produce more shares so that your income variance will decrease.
if you can mine at a higher difficulty based on your hardware, i hear it works the hardware a little less, so a tiny bit less stress on your GPU if you pick the optimum difficulty. you could always email suprnova and ask what they recommend for your rig, they are usually quick to respond