I'm seeing a lot of good advice here and just wanted to pipe in with our experience as well.
The H6 is a pretty awesome prop and it's fairly bullet proof.
As mentioned, if you can get it to a service place they can pretty much rebuild and perfect is (I have a recommendation in the VA/MD area if you need it.
When I sent my prop in for service, it was after a couple of other refurbishments, including re-burnishing the bearing races. Once we got the races replaced it was a smoother run. The tech said the prop was still in great shape overall and that it shouldn't need to be replaced for 10 or 12 more years.
On the RPM subject, at full throttle we get about 2700-2800 rpm when things are all clean and smooth .. note that if the boat is stationary .. as in stuck in a sandbar .. (another story ...) then our motor will reach 3,000 rpm. So, boat speed and the H6 are joined a bit.
One "test" is maybe be going 2 or 3 knots then slip it into reverse gear and go full throttle .. you know, like when that bozo in the bathtub tacks in front of you?
When the prop goes full flat, I think that's when you can see Max rpm.
I'm a bit contrary on the 80% number, maybe just cause I'm stingy.. but we will normally cruise (like, if we have a day or two of solid motoring) at a lower rpm to conserve fuel. Every boat is different, and we have a very "experienced" TMD22b (6500hrs) so I baby it a lot.
1800-1900rpm is our normal cruise with 1750 being a "max econ" giving us around 6kts at 4lph. We do the periodic run ups, but if you're at full operating temp our motor seems pretty happy to cruise along at about 65% or so with good mileage and no oil usage.
SM 209, Adagio
Cape Charles, VA USA