My trusty old Enya 90 FS turns a MAS 13x8 3 blade with great authority. RPM set for flying was in the mid 9k range - 9.4 to 9.6 depending on the day, how old my fuel was getting etc. The Enya is probably the best for longevity, however they no longer produce the 90 so the only way you can get one is used. Mine is currently in its 3rd airframe, now swinging a 15x6 on the nose of a Great Planes Fokker DR1. As for the Magnums, TT and ASP 4 strokes, they all sure bare an amazing similarity to the OS, which IMHO speaks volumes for the engine being copied.