For a lot of applications there are pretty straightforward calculations to meet a desired frame rate. Also I've seen UX research that established some guidelin

For a lot of applications there are pretty straightforward calculations to meet a desired frame rate. Also I've seen UX research that established some guidelines for how long something can take while still feeling responsive allowing a user to remain focused. Knowing you can achieve the required/desired performance in any given language is mostly a matter of experience solving similar problems.