I have a 1648 grumman ultra mod v jon boat. Dry weight is 275 lbs and it is being pushed by a 27hp beavertail longtail. Total weight in the boat was about 450 pounds. I was running 14-15 mph. Does this seem right? I considering buying a 23hp gatortail and wondering if I would gain speed?

I would expect i little more speed . How is the prop? What rpms are you running?Have you tried raising the governer yet? On the other hand, of course a surface drive would be faster