Here is what I do, as it is all very confusing, just as you point out.
Forget the size, name, dimensions. Simply look at the weight of the motor.
So if you have a 100g motor it will produce 300watts of power. If the plane is 3 lbs that is 100w/pound. That is great sport power for a propeller system (EDFs need more power due to inefficiencies).
This saves the hassle and overestimation of power from various motor manufacturers. Trust me many lie!
3w/g is a good power estimation. Very high quality motors (efficient) and large motors (over 500g or so) are generally in the 4-5w/g rating.
Now you really know what power the motor can produce. This will help you get the right size motor for your plane and power requirements...
This formula works wonderfully for me.