trim hole position on 40hp Tohatsu tiller

[tenacrewoods]

I'm running a 14' 70" flat bottom with 10.2X13.5 prop,850 to 900lbs and trim has 6 holes.I'm running second to last hole out and getting 30mph.If I set any lower(third hole down) then this it pushes bow down too low and any lower yet it's too hard to steer. Motor is long shaft with transom raised with 2x6 and 1/4" alum. plate on both sides(very strong) which puts cavitation plate 1/2" below bottom of boat.I read on this board you could calculate speed by taking hp,total weight, dividing then use results square root multiply by boat factor (mine 200) to get approx.speed.I don't even come close,i't should be just over 40mph.How can I get more top end?Can I go to A 10 x15 prop on 40hp Tohatsu #M40C and where can I get hand held tach to check rpms?Any advice would be appreciated.I already raised and lowered motor three times.Afraid to raise cav. plate above bottom by 1" as some have suggested,Are they sure it won't hurt motor.Would just like reasurring.Thanks for all the help I've recieved on this board.IT's GREAT!<br /> Mike E