The Sundowner in the thread you linked to is a racer. Race pilots aren't known for try to keep their stuff long, they just want as much speed as possible, and if they burn up an engine in the process... oh well. (Nascar engines last for one race before being completely rebuilt, right?)

As far as "Practical RPM" goes, yes, you can get 16,000 RPM out of those engines when they are turning a ducted fan (Which is onlt a diametr of about 3 or 4 inches) and yes, you WILL be replacing them often.

They will not, and SHOULD NOT turn a propeller anywhere near that speed. At least, not if you still want to use it in a year or two from now.