And I was thinking a third idea

With a temp sensor installed, I can use the feedback from it to maintain the set temperature (ie, 205*). If the temp continues to rise, fan speed would increase to full speed in 5 or 10% increments. Likewise at idle, it may only need 10% to keep 205*, so why have the extra noise and current draw.

Or, I make the minimum speed 30-40%, so at idle it will still be able to lower the temp and kick the fan off for a little bit, while minimizing noise & current draw.

For AC it would still kick to full speed.

In theory if the feedback loop is correct, if you hit the highway, it should cool off from the increased airflow, with the controller responding with a lower fan speed. Continue until the temp drops enough to turn the fan off.

I may have to make a video of the fan at low speed. It's almost silent

As for the hardware changes needed... I basically need to start over The current board I sent Andrew can't get a clock speed low enough that can generate the speed of duty cycle needed. The basic design stays the same, it will just have a different microcontroller controlling it, which is all transparent to the end user.