[RC-Monster Mike]

I agree with the previous post, but would like to add to it. While a high top speed can be reached with a small motor, the motor will eventually fail if it is driven this hard continuously (I have "failed a few motors"). For continued high speed, a larger motor can dissipate the heat better and will last longer. Higher voltage (like Lipos) will also help keep the heat/amp draw down, which may also lead to increased reliability (as long as the motor is not over revved). I will also say that weight may not be a big factor, but it is part of the equation. It takes more energy to move more mass.