No doubt about the engine noise. I've heard sport jets are loud. Then again, I can't see how much louder they can be than all the 2 stroke outboards on the river. Mine is pretty loud. I've seriously considered sport jets, and am not opposed to it at all. My questions about those are really more about life expectancy vs an outboard. I would really like to have one in a boat. I haven't been able to find much info on what it would cost to get a new one. It makes a lot of sense though to go for an extra 100 hp for the same weight.
Different manufacturers go to different lengths to quite them down. Honestly my 200 isn't that bad and the performance is great. As far as life expectancy goes it's like anything else. Take care of it with good maintenance. They took care of the reed issues the earlier ones had. Biggest failure u will hear about is the low pressure fuel pump or lift pump. It's a cheap pump and an easy fix. Most carry a spare so it can be changed on the water. The sport jet boats are fun. I was just thinking v8 because of your need to be hauling 6 adults at times plus some gear I'd imagine. The sport jets can haul that weight but my boat loses a little bit of its sporty feel when weighed down. I guess the best advice I can give is test drive whatever you can and go with what feels best.
That makes it tough if u can't drive a few different boats to see what you like best. Custom builder should be able to point you in the right direction though. If you do end up going the sport jet route, be sure to get a stomp grate for clearing the pump of debris. I don't use mine often but it's real convenient when the intake grate clogs. Only other thing to be aware of with the sport jets is the stock reverse bucket sucks. U can have extensions welded to the bucket or go with an aftermarket bucket that will actually give u reverse. Good luck with it.
For that boat and 5-6 people you absolutely need the 250 guaranteed. If you do the inboard maybe not.
Im almost certain now the boat will have a sport jet. I priced them and have several choices of dealers nearby to install and rig it for me. It wont be that boat unless its still available later this year. My dear bride has put the brakes on watersports until we finish building. But that gives me plenty of time to figure out a floor plan.