kV is the RPM's per volt going in to the motor, so in your example a 5700 kV motor on 11.1 volts will give you 63,270 RPM at best efficiency. It won't give you power output.
The power ratings seem to be getting more guarded by most brushless motor suppliers now. Don't know why, it's always been the best way of guaging motors along with peak RPM and peak Torque.