i'm using the default frequency maybe 800 and it is working for the fans and doser (connected through Dual Large Power MOS Transistor Driving Module)
the Noctua is somewhat noisy when the power goes above 50% (used to cool the pi case), the arctic f12 is quieter
you can try different frequencies and see how it goes
I'll do some testing before going down another route. I'm mostly worried about added noise due to the fact that the fans will be running 24/7 at different speeds. The industry standard for the signal pwm is 25kHz +-3k mostly because it pushes the signal above the audible range.

