[Afton]

There is no optimum number. There are optimum numbers for specific goals. List your goals, your hormonal and diet context, some genetic factors, and then people could propose optimal reps for you.

Unfortunately, a lot of exercise studies use untrained people. How that extends to even moderately trained people is usually pretty problematic. I'd say "forget it, just listen to people that have been doing it for a couple of decades" is probably better advice.

The primary mover of all set-and-rep ranges is going to be goals and hormonal context, so make sure that when taking advice from someone, know what they think those two things are.