Yamaha90 optimal height?

Galia 515 bowrider & Yamaha 90 2-stroke optimal height testing.
3rd hole seems to be the best with original 17" aluminium prop, but 4rd hole is also strong alternative - but only with steel prop.

Btw. when it comes to rpms, i have a doubt about my tachometer: 17" Ballistic prop + 5100 rpm + 34,8 knots + gear ratio 13:26 = only 2,5% calculative slip ... ?
http://continuouswave.com/cgi-bin/pro...
I quess the real rpms are appr. 5300 - 5400.

A good dialog about engine height (with steel props):
http://www.veradoclub.com/smf/index.p...

I think my boat won't go faster than 35 knots with 90hp. I need more horsepower (boat maximum is 150 hp) - or lighter boat ;) On the other hand, with normal cruising speed (28knots) Yamaha 90 hp is pretty quiet and economical.