So today since it was calm, I threw 2 people in the back of the boat and measured the static height per mercruiser. I get ~11.5 inches. If we move to normal seating positions it climbs to ~13 inches. So it looks like I will throw in a set of 3 inch risers to play it safe. After measuring I don't think I have room to go much taller so that should get me okay. I'll measure more tomorrow.