With the weight of that boat, you would be fine either way. I think the LT will help reduce your chances of punctures. I know the GYSA in the LT tire also have an E range, but your boat I don't think will require you to go that extreme. There are others on this forum that tow heavy camp trailers that the E range LT tire would be more beneficial for them.
As for the OEM long trails, I'd never buy those. Only reason I had them was because they came with the car. They were horrible in wet weather and they didn't even last 30k miles on my Pathfinder. My duratracs I have on now have been great in wet, snow, and off road. Have lasted over 40k miles. The only reason I plan to go with the GYSA when I get new tires are my wife drives the pathfinder the most and the GYSA I think I can get more mileage out of them while not sacrificing too much performance.