I have an 83 150hp merc outboard, its on a 20 foot ski centurion, a friend of mine was tellin me not to run it over 4500 rpm, when its trimmed all the way down and punched it runs about 5000 rpm, and then with a little trim it hits 6000 no problem, it has a stainless steel vengeance prop, that is a 17 pitch. I also have a 5 blade stainless 19 pitch prop as a spare, im guessing thats for power for skiing, not top end.he said if i put a 20-21 pitch i will get the mph without the high rpm's, then someone else told me they ran their 150 merc at 6000 rpm all day, im confused anyone have any advice? I dont wanna blow it up, the motor is a black max motor.