[Hawiian Cadder]

That looks awesome. Keep in mind that if you are running all 4 motors off a single battery It may create a voltage drop and causing inaccuracy your efficiency calculation, you could use a multimeter to find the actual voltage and then use the RPM/Volt given for the motor to calculate what the free speed in that scenario would be, and calculate a more accurate and probably better efficiency, even if the voltage were only a few tenths of a volt below 12 it could push your efficiency up a couple percent when taken into consideration.