380 class motor is standard amongst smaller RC vehicles and boats. Nevertheless, 380 is simpler to get overheated and is much less succesful torque-wise.
390 is more and more used however there are simply too many variations. Some won’t ship something significant except beneath 12V or 3S, which isn’t attainable given the limitation of most brushed ESCs.
The picture under reveals one (390-6221) which may be very highly effective even with 2S energy. 
