Just bought an 18ft Shadow today. It has an older envinrude xp 150, 6 in jack plate, and 4 blade prop. I want to get an early 90's merc or mariner 200, but until then, what would be the best set up with current accessories? Oh, and haven't had a chance to get it on the water yet, but owner said top end was 53-55. Sounds slow for this boat?

Thanks for any advice.