From personal experience...
Although I own a smaller Triumph, I can say that "bigger is better" in both boat size and engine size.
Dealers tend to install a midrange engine that will, under most circumstances, perform okay. They do this to reduce the overall cost of the boat. But, when you need that extra HP, it's just not there.
I went with the lightest and most HP I could install on the boat (70hp two stroke Yamaha) and I'm very happy with it.
I have had divers off my boat, but due to size, I can only hold two divers plus gear and a captain to stay aboard.
Hope this helps.
BarryB, AP
Aboard "SURPRISE"