Yes, the engine is set a little rich in the video rather than squeezing everything out of it, and it would creep up towards 18900rpm when left longer at full throttle. The video was more for my own documentation of throttle response etc in order to compare with the running with the pipe on it, but then I somehow screwed that up when I used the camera.

Back to prop loads, I plotted the data for the APC 5.7x3 prop in a similar way, and there the data file seems to be correct up to 23000rpm at least (didn't plot higher). There is only a slight discrepancy in the constant I guess;