Anything over 40 hp is pretty much wasted money. Your boat needs somewhere between 30 and 40 shaft horsepower to make seven knots in calm and rough conditions respectively. At 6.5 knots you don't need more than 20 hp. Vetus and Westerbeke are both Mitsubishi blocks and are pretty much the same engine. One option would be the Westerbeke 44C which is rated at 38 hp at 3,000 rpms. If you wanted more power, the Westerbeke 55D is rated at 48 hp at 2,600 rpms, but I think that is simply a waste of money. The comparable Vetus engine is the 4.17. Other options you might consider are the Beta and the Nanni. Both are Kubota based in the HP range you want. I wouldn't discount Volvo out of hand. The new Volvo engines are completely different beasts from the old ones. A Volvo D2-40 gives 40 hp at 3200 rpms in a compact, light 4 cylinder package