How to calculate frequency for PWM design
If you need between 1 and 1023 pulses in a ~100usec period, then your PWM clock needs to be 10.24MHz (10MHz should be fine). 

The frequency would thus be fixed (9.766kHz) but the width (that's the 'W' in PWM) of the pulses would vary from 0 to 1023 x 100ns units wide in a 1024ns total mark + space width.