Comparing apples and oranges? or electric motors and internal combustion engines?

When the electric motor is loaded more and more, it simply pulls more and more electricity until it reaches some equilibrium or burns out the battery, esc, or itself. When the glow engine is loaded more and more it will reach it's max chamber pressures and if the load continues to increase, start to lose rpm from higher heat/friction/whatever.

So what stops the electric motor from increasing the thrust of that mass of props, all of which produce exactly the same thrust? It stops itself from producing more thrust, just as it does when there is less load. It has reached a load it can handle and does so.

So the electric motor isn't actually proving anything about the props, it's proving it can overcome whatever aero problems all the tested props have to produce identical work from all, to produce it's max work.

My take on the electric motor test is that it's not telling the efficiency of the props at all, but that it's telling you how strong the motor was designed to be, and that you have a sufficient battery for that motor. If I wanted to test the efficiency of the props, I'd run them all through a series of rpms and record the thrust at selected rpms. And I'd use a sufficiently large motor for the test. Basically, I can see the motor test as a test designed for comparing the efficiency of a bunch of electric motors.

But then, I consider almost all static test results for props of little value. It's more efficient to fly them puppies to see how they're going to fly.