As for brushless motors you need to take a serious catalog of a manufacturer and read carefully the explanation of curves and various types of winding. on the forum we posted here and the explanations.
Below are my notes for alternating current square engines, extensible to those in continuous current and brushless.
generally they are all engines that have constant torque from 0rpm to the basic value of the engine that could be a classic 1450rpm for a 4poli alternating. then from the nominal regimen value you have a constant power trait (then decreasing torque) up to a regimen n1 with generally linear behaviour and then you go down fearfully.
your load application must be under the torque/regime curve and at the power/regime curve.
It is also important how the engine is managed, with inverter, under the nominal current or above, at intervals or not.
practical example:
application where your engine moves a reducer and a screw axis with known accelerations and known masses.
We will have qualitatively that to go to the required speed you have to do it with a certain acceleration, so you will need 10nm to 1000rpm to accelerate and maybe 8nm to stay almost in speed up to 1700rpm.
well, once you choose the blablablabla mechanical reducer you will have to choose a motor that has pairs equal to or greater than 10nm to 1000rpm and 8nm to 1700rpm.
turn to the hand choose the smaller one among the models that meet the need for the load.