What is the ECM machines speed and torque motor curve/characteristics? How does it compare to others?

When an ECM machine is commutated in the same fashion as a brushed DC motor, based on shaft position, the torque-speed curve is flat and linear. This curve is similar to a conventional brushless DC motor, but without the intermittent cogging torque zone.
Complete absence of cogging torque is an outstanding feature of the ECM machine.