9920/8L questions and more

[RC-Monster Mike]

The 8L can run on 14 cells, but it is happier on 12 is all. For a heavy truck, the xl motors are more up to the task, but even the "L" motor can easily get you into the 40s with the right batteries(batteries are the power-the motor only transfers this power to the truck-better batteries=better power). If you want to go 40+ all the time, the xl motors are a better choice.