perhaps someone with a lot more motor knowledge like jraef can give you a number but from my experience it's not that simple. assuming you are speaking of motor short-circuit/ground fault protection, I have found the range is so dependent on variables that it's difficult to select. One thing that should help you is to check the LRA Code and Table 430.7(B), but the type of load and starting torque varies so much I could not guesstimate a "average". I always leaned toward the high end but as your point out that can change your breaker frame size and cost considerably.
I was always taught to respect my elders. Only problem is there days there are so few of them.