NOAH - you can figure out the cruising speed by using a prop calc . . . just plug in the numbers for a 17pitch prop @4000rpm and assume a prop slip of about 12 - 15% for an depends on load, wind, and waves (if you have a top then .15 - .18 - maybe more) The gear ratio of your 225 (1.81). I've found these calcs to be very accurate using many different props. The only thing you won't know until you test out the prop is the WOT rpm's . . . just make sure that you prop the boat on the upper end of recommend RPM range (5500'ish)
http://www.rbbi.com/folders/prop/propcalc.htm