The answer to this question is a little bit tricky. But here’s a plain and simple explanation on this matter that should be easy to understand:
Stock-Low optimization method offers the best gaming performance while maintaining the best possible graphics quality.
Ultra-Low optimization method offers the perfect balance of gaming performance and graphics quality.
Ultimate-Low optimization method offers the best possible gaming performance while still managing to deliver decent graphics quality.
Plain-Low optimization method offers the best possible gaming performance while maintaining acceptable graphics quality.
Potato-Low optimization method offers the best possible gaming performance while sacrificing the graphics quality the most.