I think most engine manufacturers are worried about over propping their engines if only for the loads at wide open throttle. Unfortunately with a fixed pitch prop this leaves a big sag in the load curve in the mid RPM range. At the RPM most of us would prefer cruising, the engine is under a lighter load than is ideal. I'm new to this sailing thing and displacement hulls, but I wish I had a dime for every person that has told me "Yanmars like to be run at higher RPM's". I'll bet this has to do with soot buildup in the lighter loaded RPM range because of the lower cylinder pressures and temperatures.
In my case I was told that the target RPM during sea trials for the OC45 and the 4JH5E was 3150, right about where I am at, a full 150 above the max rated 3000. This may provide a margin of safety regarding engine loading for the manufacturer but does the owner a great disservice as far as how it will actually be operated. For example If I added another inch of pitch I would probably drop down to about 2900. This should be well within the acceptable range of operation, and make for a more comfortable cruising experience. Instead I'm read the script of fear with regards to the manufacturer and warranty when considering a prop change. It's BS as far as I'm concerned.
I was not aware the Gori's had an overdrive feature, but it makes a lot of sense. My question is does it not drop out at higher RPM and loads? In which case the loading would be a non-issue. I also considered the Autoprop but the tests I read showed only a marginal improvement in the mid cruise RPM range versus a Flex-o-fold, with inferior performance in other areas, specifically slightly more drag while sailing. Since the primary purpose of my boat is sailing and not motoring I am leaning toward the Flex-o-fold, and it's about 2K cheaper.