Maxum2000 - That will depend on what you have loaded in the boat and the props you have on the outdrive and the condition of your hull. Assuming you have everything "stock" and a nicely polished hull (not painted), with full fuel tank, full freshwater tank, the usual boat safety equipment, a couple passengers, and a cooler of your favorite beverages, you should be getting close to 50+MPH out of that 7.4L. If I have half tanks and no passengers, and can easily get 50+ out of mine.
You should be able to get up and hold the boat on plane at around 22mph. She cruises very nicely without draining your fuel tank at 27-30mph.