Try "Auto" and uncheck "Limit by FPS". This has always been the best combo for me. Tested SMS myself just now. With 30 FPS + Limit by FPS, it speeds up 2x. Unticking Limit by FPS reduces it to 50%. Auto without Limit by FPS works fine. I think 30 FPS games are picky in this regard; Xenoblade Chronicles does the same thing for me.
If Auto + unchecking "Limit by FPS" does not work for you, try 60 FPS + "Limit by FPS". It's a sort of hack-ish, but that's what I used to do in Xenoblade Chronicles before I knew better.
If Auto + unchecking "Limit by FPS" does not work for you, try 60 FPS + "Limit by FPS". It's a sort of hack-ish, but that's what I used to do in Xenoblade Chronicles before I knew better.