When doing distance runs, even large fast powerboats almost always do the delivery
at sub-planing speeds. The fuel
burn climbs exponentially as speed goes up linerally. So each additional knot
of speed may cost you bug in fuel
My thought right now is to buy what you plan on using now. The boat you would want to cruise
the Carribean on is a very different one than a live aboard. And making a run to Hawaii
... As mentioned there aren't a lot of power boats that can safely make that passage
. Few boats actually carry the fuel reserves to get half way there, let alone all the way.
For a long distance cruiser (with long range) you need to be looking at boats with a top speed of 8-10kn, very long, and narrow, with a tucked transom. In fact a power boat
that looks a lot like a sailboat hull
. This shape is easily driven, which means the boat doesn't need much power to make good headway.
The best example of this I know is the FPB by Steve Dashew. At $1 mill plus they are expensive, but the 64' only has an installed 120 or so Hp to make 10kn. Everything after that is just fuel burn.