I have had an Optima Blue Top for 7 years now running a 150HP and always worked well however the Charger would never seem to know when the battery was full. Checked it earlier this year and its capacity was down to 95% so put it in the tinnie and now run the Seamaster. The only other issue I had with the blue top was it certainly dragged down when using the electric winch.
Your brother in law is a battery specialist both marine and deep cyclem I'd be hitting him up for some solid advice.
Maybe they just hold the worlds best surface charge
Don’t take my advice just google search optima battery issues then decide