I don't have any proof, but those 65/55 watt difference are probably just marketing scheme. Even if it's true, your ballast might not necessarily drive your bulbs to 65 Watt. If you want optimum lightning, just clean the salt spray from your bulb once in awhile. Also, sand the inside of the canopy and paint it a marine waterproof white paint. If you have enough rock work, just keep the higher light demand corals on top, and lower light demand corals on the bottom. I would run your current 2 bulbs setup 1st to check for any heat problem b4 you decide add any more bulb.
Look at all those live rocks on the beach at Florida's state park!