There seem to be two schools of thought on the best PWM frequency to use. One school favors relatively low frequencies, as you mention. The other school goes to something like 20 KHz (e.g., 4QD). One rationale for the lower frequencies is that the motor's field and/or armature can keep up with the lower frequency. Those who use the higher frequencies essentially say so what, we are only interested in the average power.
In the few applications that I have made, I went with the higher frequency, namely because you can't hear it. A motor at 2.4 KHz can be a real annoyance. Many of the controllers for small model airplane motors are also going to the higher frequencies. John