A .60 two stroke is not comparable to a .90 four stroke! The four stroke is more powerfull! Years ago they allowed the pattern guys to use 15cc sized 4 strokes while the limit for two strokes was 10 cc. Well at the time maybe they were comparable but with the next generation of 4 strokes (which came out immediatly after this rulling) the pattern guys switched to the 4-strokes. A typical sport .60 is probably more compareable to a .80 4-stroke.