Just to be certain, you must check WOT rpm under load. If you try to do so at the dock, in neutral, you will get a different result and its inapplicable.
When you are overpitched, you will get too low a result. I will echo that you confirm the accuracy of the tach, as they are indeed notoriously wrong. Lancelot, it could even be the case with yours.
Backpressure from overpitch is just clearly bad for a motor over the long term. Some engines will be more finicky than others, but getting way with it is like deciding to take up smoking because you know of one 90 year old that smoked their entire life.
Ironically, overpitching the prop helps maneuverability around the dock. That will probably convince some to take their chances.
Being overpitched at cruising speed for a lengthy period of time, probably isn't that bad. But getting there is just like leaving a stop sign in 4th gear. Doing that thousands of times just ain't good.
Not sure why one would be fixated on cruising at a given rpm. It should be whatever the motor wants to be at proper settings. Don't like the noise? Well that's obvious, but there are no engine noises that I'm good with. Necessary evil.