When I go to render, if I click on the custom button, it opens up some tabs. On the Video tab, there is a slider for video quality that is set in the middle by default. I noticed this slider's position doesn't change when I set best quality versus good quality on the main rendering menu. Has anyone used this slider at the highest setting, and does it make much differnce in quality or rendering speed?

Always slide it to the highest setting, that is what I have found from some research on it when I had the same rendering question.