Just thought I'd chip in on this one, we've spent the last couple of weekends messing around on the taw/torridge estuary in our aerotec 420. I've been doing some tweaking, the 420 takes a long shaft outboard and I've got our 15 hp mariner 2 stroke packed up by 30mm on the transom and this has pretty much got rid of the spray issue.
The 15 HP gets 2 large adults, a kid, dog and luggage up on the plane easily. Don't think I'd bother with a bigger engine now unless we had a trailer. As it is, I can easily hand launch it and pull it up beaches on the transom wheels. It's a lovely boat, such a lot of fun and if this one ever bites the dust I'd replace it with another aerotec straight away