rpm question

[jabberjaw]

hey guys im new here and im looking for some info on my engine, cant seem to find anything anywhere. i have an 86 dt150 on my 19ft stratos and it has a 4 blade prop with not one marking on it so i have no clue the pitch or brand . here is where im at, gps'd im going 55-56 mph at 7000 rpm's which seems a bit high since my friends 2.5 merc is running around there on his tunnel hull. id like to know the max operating rpm on the dt15 and also does the dt200 turn anymore max rpm than the 150? thanks...