Dev; I've never run anymore than a single deep cycle Marine/RV battery on my 16 SC. I keep it charged in my basement over the off season, and trade it in every three years for new. Knock on wood, I've never had a failure. That said, reading your old post has convinced me; if I ever add a second battery, it would probably be another rugged deep cycle. The way you describe the sensitive nature of those thin plate starter batteries, it just seems to make more sense to me......especially since I'm only talking about cranking a 60 HP motor. Just not crazy about (what I call) a "car" battery in a boat.
Yat