[BrianG]

Not necessarily. People generally shoot for higher voltage so a motor with more turns can be used for better runtimes yet keep the power. If you use only 7.2v, you'll need a fast motor to get the speed you want. That kind of motor will have a lower turn count, but will require high currents. Runtime will suffer and you'll need strong batteries to deliver the current. If you use 14 cells (16.8v), you can choose a motor that has a lower kv rating and runtime will be better. Some people even go higher voltage for more speed if you want to get crazy (over 40mph). Just keep the max total motor rpm around 35,000-40,000 rpm for whatever turn motor you select.