Sounds like we are in violent agreement. Of course in the video, it's screaming. It's loaded well below the range specified by the manufacturer just as this shows it would be. I should have shown that his prop would show a load of 317383... a good deal below the recommended range. As far as all the other factors, of course they are there but for the most part they change little and aren't under my control. I just look at the range specified by the manufacturers listed props for THIS engine. Quite correctly, it was pointed out ths is the load on any engine but the range to pay attention to is defined by the recommended props. Finally, while I would agree the 17x6 is a nice match for this engine in terms of putting the engine at a nice compromise between torque and horsepower (it's what I run because it fits the purpose of my RV-4... moderate speed and lots of torque), saying it is best is to miss the point. Best is defined by what you want out of the motor. Most of us like pull/torque but others want more speed and which airframe you install it on and what you want it to do would influence the prop selection. I'm just showing an easy way to figure out if a prop keeps you within the range of loading the manufacturer is pointing you toward and therefore likely to keep your engine "intact" while still giving you flexibility to chose what is best for your application. If I had a P-51 racer I'd opt for picking up something in the 15-10 range or even a 14-11 or 14-12. None of these are listed by the manufacturer but would keep RPMs in the range the manufacturer recommends and give me much more speed than the 17x6. Just trying to give folks some other options... and a way to know they are not likely to damage the engine when doing so. Or at least if they want to go with a 12.5x13 they will have an idea just how much outside the normal range they are likely to be! It's a testament to the DLE that it is holding together when over-revving like that. As we all are finding out, on average these are tough little motors.