I went down the same road a few months ago; personally, I love my Wattsup meter. It gives instantaneous readings of amp draw and watts of power, and will also check your charger's performance. If your plane will carry 2.3 oz payload you can put it in your airplane and check the in-flight numbers when you land.

If you have the continuous amp-draw numbers for your motor, you could buy a battery pack and ESC that would supply the right amount of amps, and just go up in prop size until the motor temp starts to get up into the hot range. That will get you in the ballpark, but it is comforting to know EXACTLY what is going through the wires....Jim

PS I don't have any specs, but the new Eflite watt meter from Horizon is significantly less expensive than some others. JB