Motor for precise low speed motion but also capable of high speeds
Most hobby ESC operate its motor sensorless. So the RPM is unstable to detect at cetain level. It means correct speed control isn' easy at low speed because the sensoless control would work some level of speed.

Stepper motor is good at position application. If you want use stepper motor as speed control, you should apply vector control instead of open loop. Then you will get more than 600 RPM.