In the 'old days' I shopped JC Whitney catalog for speed secrets to make my 1961 VW Bug fast (not actually doable (without $$$$) at that time (1967) no matter what you did!). My belief was you add this $45 part, and that $15 part, add the projected performance increase together, and have that magic where a VW can pass a semi on a highway against a headwind (was VERY difficult)!
This is kinda the same in our brushless motors. Most think you put in a high gauss rotor in a low inductance stator, make the rotor to sensor clearance tight, confirm the sensors were 120 degrees from each other, and you have an unbeatable motor for the class.
The above is not quite right. Besides physical tolerances in the components, each components' electrical characteristics influence the other specs every time you change end clearance, or rotor, or other component in the motor. For example, I was building a 'max effort' Team build in a drag motor. Rotor to stator clearance is very critical as well as well as rotor length and magnet asymmetry. I find a great rotor to go with a near perfect sensor, shim and assemble, and now the sensor deviation is out of whack (and this was a very good sensor when tested in another motor). Again, motor pulled apart, and sorting begins again to find another near perfect sensor which will work in this motor to 'max effort' Team specs. Three hours later I am finally done on this one motor.
The moral is give your motor builder a break (I hope I am your motor builder!!) as she takes time to get your custom motor to you and be particular if you disassemble your motor. I pride myself in delivering what is expected; even in a normal race motor my tolerances are tighter than most other builders to give you a quality motor. And if you are changing bearings, or a rotor in your existing motor make sure your shims are put back from where they come from. Your motor will thank you!