Is there a difference in performance between a the default scaling option and selecting a resolution?
Solution 1:
Changing your resolution doesn't really affect performance. What will give the effect of improving or reducing performance is refresh rate. A higher refresh rate will smooth things out giving you the "feeling" that things are much faster. A lower one will make things look more "jumpy" thus giving the effect of lagging performance.
The default scaling is what macOS has determined to be the "best" optically for your particular setup.