Choosing the right motor to control mirrors
You are comparing potatoes and apples. The limits of stepper motors are known, while you are comparing servo motors, which indeed are RC servos, not the PMSM or BLD servos. In the link you can see BLDC motors. Now it is up to you to choose a BLDC or PMSM motor and driver. 
The you' ll need a master controller, which will send position setpoint with known speed, acceleration - aka trajectory generator. Each driver has to correct the actual position vs. setpoint position with the use of cascaded control loops - position, velocity, current loops. 



This cascaded controll loop has also feedforward paths, like setpoint velocity from trajectory planer is fed forward to the velocity loop, regardeless what is the position error. In the same manner you have a torque/current feedforward path, derived from velocity setpoint. The required feedforward torque is: \$ T= J\cdot\alpha\$, where \$J\$ is the moment of inertia of the system: motor's rotor inertia + transformed inertia of the load. \$\alpha\$ is the angular acceleration \$\alpha=\dfrac{d\Omega}{dt}\$, where \$\Omega\$ is the velocity setpoint.
A high end servo is updating the current controller at aprox. 50 micro seconds, the velocity controller at 100 micro seconds, and the position controller at 500 micro seconds or more, it depends on the trajectroy planner.