Another way to approach your question:
Assuming CC max designed speed is both safe and legal, and that CC’s focus is not wasting money on over building/engineering their golf cart so that they can remain competitive, let’s work backwards from CC’s max speed of 20mph (their additional paid speed code controller update.)
Using the below calculator you get 4500 rpm’s (gear ratio 12, tire size 18 )
http://www.buggiesgonewild.com/speed-calculator.php