[BrianG]

So, based on the previous posts; find the voltage to use by simply dividing the max rpm (35 to 40k) by the kv value of the motor.

Using 35k rpm as the max rpm:
For a motor with a kv of 2000 rpm/v, you'd want to use 17.5v.
For a motor with a kv of 1000 rpm/v, you'd want to use 35v.

Motors with lower kv values will have more windings, therefore will require less current. However, since you are using higher voltage with less current, the total power will be roughly the same as a motor using lower voltage but higher current.