A gear ratio is simply that - a ratio. It is generally true that if the ratio is high (2:1) then the car goes faster in a straight line and accelerates slower, and if it is low (4:1) then the car accelerates faster and has a lower top speed given the same motor is in use.
How you get that ratio makes no difference to that generality. You can run 20:80 to get 4:1, or you can run 21:84, or 22:88... However, it does make a difference to efficiency. The larger the spur and pinion you can mesh, the more teeth are in contact, and the lower the rubbing velocity of one tooth over the other. This means that the mesh is 'stronger' and less liable to fail under shock loads, and that the gear train is more efficient. Sounds great, but...
Since we have so much power, and fuel in the tank (battery capacity) we don't much care about efficiency in order to win the race. So, the best reason for using the largest possible combination is to give an extra margin of strength to the gear mesh. If you had the choice above, choose 22:88.
The ratio effect is only a general rule because if you let a motor rev too much it will get hot, and if you are trying to get weight on the move you need torque, not power. Sometimes, you will get more acceleration by using the torque available and run a higher gear ratio, and sometimes you will get more speed if you gear down and let the motor rev. That's why you run higher wind motors (10.5) at higher ratios, because they have more torque, and you can't get the power out of a 5.5 unless you gear it down and let it rev. HTH
