Brushless motors are often marketed with their Kv constant (motor velocity constant) which signifies how many revolutions per minute the motor will produce with no load for each 1 volt applied to it.
For example, a 1,000 Kv motor under a 5V load would spin at (roughly) 5,000 rpm.
Therefore, a motor with a higher Kv rating is likely to have a higher top speed than a motor with a lower Kv rating. That said, these numbers are produced under no load, in laboratory conditions, so some variability will naturally occur.
Please note, this Kv is not kV, which is the abbreviation for kilovolt. Nothing on your RC car should be happening in the kilovolt range. :D
For more information on how this affects an RC car's speed and acceleration, see our article on motors.