Plan your flow for what you want to have eventually.
I'm at 2400 gph in my 55, buuut you wouldn't know it from the tank. I have several small ph's positioned behind rocks so its totes diff from one big fan at either end. There's lots of spots where it's barely moving so the fish can rest, and chill coral can live, but most of the rock is kept free of detritus. I like the all over turbulence better than a couple jet engines. I'm shooting for a lot of LPS, idk what yours need. But you gotta have a bare minimum so the bottom water gets wooshed up and into the overflow so your gas exchange isn't compromised.
I just kept adding the $10 SunSun power heads until I got it how I like it. Yay Amazon prime!
I don't count the overflow, that's separate from tank flow.