@James the only post I saw on thesamba said 2x the engine RPM. Several folks were talking about regularly going to 8000 RPM with balanced and aligned fans. General wisdom is that the original German fan assemblies are best (with TIG welding).
Again, I suspect mine was a fluke of over a decade of close exposure to mist from the surf. Our house is 1/2 mile up the hill from the beach and still have to wire brush and repaint outdoor steel items every 2 years.