Performance numbers from Yamaha are readily available for this combination. http://www.yamaha-motor.com/assets/products/otb/bulletins/bulletin_otb_4StrokePerf_HPV6_150hp_03-87-PKR-C.pdf
40 mph top end and cruise at 30 mph while getting 3.75 MPG is pretty good IMHO.
Jason
BTW nice boat at a...