> It’s not in the 20k unless your population is extremely high

Common misconception. Population size has almost nothing to do with the necessary sample size. (It does enter into the finite population correction factor, but that's only really relevant if you have a small population, not a large one.)

...actually, come to think of it, you meant to write "unless your population variance is extremely high", right?

Right and the methods I had in mind were the usual ones: proportion-based, mean-based, and power analysis, depending on what’s being measured. Thanks for catching that