There are many reports high hour usage on 4 stroke outboards. Remember that these are motors that are mostly run in commercial use--run every day, and have very good maintance. Some have a fair number at lower RPM.
Fishing Guide boats, offshore fishing boats, Coast Guard, Marine Patrols, some salvage and towing services all have reported engine hours in this range--a number of the Johnsuzuki (140 Suzuki with Johnson logo) in the 6000 to 7000 range. Same for Yahamas.