Gonzo, if you're looking at about 300 HP and want a modern design take a look at the Yanmar 6LPA-STP.
http://www.ellisboat.com/docs/Engines/6LPA-STP.pdf
My boat's builder is using them now and claims it will push my boat up to 25 MPH (about 22 knots). My boat is about half the weight of yours.
I too want more power and was playing with one of those prop calculators. I put in my boats current horse power, length and beam. It was pretty close predicting the speed I actually get. When I plugged in the 315 HP of the Yanmar darned if it didn't come up with 22 knots. You may want to play with one of those calculators.