If you read further in Greg's post, you'll see that his system was drawing over 80 Amps at full throttle. That's why he had the thermal shutdown problem. Even at partial throttle, the pulses going between the motor and ESC will still be at 80 Amps, and the ESC will still heat up.

As long as you run the ESC within its specified limits, you will be okay. Greg was running a 20+lb airplane with enough power for wild aerobatics, and possibly 3D. I believe the figure was 3000+ Watts at 80 Amps. You'll be powering a heavy-metal warbird with an all-up weight of around 15-16 pounds. For that, you'll need around 1500-1600 Watts. On a 10S LiPoly, that's only about 45 Amps.

The Actro 40-5 will buy you one of the following over the 40-6:
1. It will spin the same prop at a higher RPM, and draw more Amps.
2. It will spin a smaller prop at a higher RPM, drawing the same Amps.

Unfortunately, I don't know of any application tables for these motors, or any testing data. Hobby Lobby's pretty vague in their specifications on the motor too. I know that either motor will easily do what you want as far as Watts go, but if the 40-6 does it with a 21" prop, for example, you'd be better off with the 40-5. Even the 40-5 might not be "hot" enough to turn a prop within your diameter limits.