My last boat (34' cat) I ran 6.5" coax Focal speakers. They were awesome and I had tot tow the boat through some storms without the cover, no damage to the speakers, although i did have billet speaker covers with screens, but they still got wet sometimes.
My new boat is a 370SS Formula and I am installing only 3 pairs in this boat and putting about 800 watts to them. In my cat I had 4 pairs and for the cruiser, 3 pairs is more than enough for a very loud and CLEAR sound. The 4 pairs of Focal were louder and more clear than 6 pairs of MB Quart with more power.
I am running the Focal without question, as it is one of the best I have ever owned, and I have tried a ton of different stuff (MB Quart, Rockford, JL, Diamond).