How much speed you improve by adding the 3rd engine? how does it take the rough water in comparison with 2 engines, thinking on adding a 3rd 280 or changing to 3 liters on my 30'

I gained a solid 10 mph and a huge gain in acceleration. I used triple 2.5 300 drags with15" midsections though.
I never had the opportunity to run it in anything over 2 ft chop after the conversion.
It handled better with the triple set up, and I never regretted adding the third engine