I have something similar to this one
9-50V 40A DC Motor Speed Control Module PWM HHO RC Controller 12V 24V 48V 2000W | eBay in my 85, not because of anything wrong with the resistor pack, but because of noise. With the fixed speeds, middle is too loud, low is ok noise wise but not enough air flow. With the PWM, I can dial in exactly what I need in loudness/ airflow balance.
The one I linked to ships from China so it may be a long wait. If you want one faster, you can get one shipped from the US but you'll pay 3x more for the same thing.