I think the first step is trying to pin down what it is that you're looking for specifically. What kind of speed, what type of use you want out of your boat, rpm range, budget, that kind of thing. There's a big difference between 600 and 800hp, in both performance and expense. Then it seems your best bet after that would be to find a reputable engine builder who understands your combination (hull, drive, type of use, etc) and what your goals are, and can give you the best value and performance for your dollar. It really boils down to what you want, and are willing to spend.