Another option for teams electing to run the 6 volt motor is to limit the peak voltage going into the PWM to avoid over heating the motor. I tested running a Blue Victor using a 6 volt supply and it appeared to run well. I am not an EE, so I can't say if this is safe for the PWM - I would continue to run the PWM fan on a separate 12v circuit. I also am not sure if this violates some other safety/construction rule. So I'd appreciate it if an EE and someone from the rules committee would chime in. I checked on Digikey, and there are many solid state voltage regulators at 5, 6, 7 volts and up to 20 amps. There is a cheap hobbiest trick that uses 2 diodes to float the center tap of a 5 volt regulator. This should result in a 6.2 volt output on the regulated supply.

Even the 12v FP motors and transmissions tend to heat up in competition - so I would consider using a fan to cool them. A simple trick is to position the PWM near the motor so that air is always blowing over the motor.