I have been using the group 34 dual purpose for my batteries, I think D34M. I also use one for my 175 EFI, but it is a 2.5 liter block, not sure how much cranking amps, if any more, you would need for a 3.0 liter 200. I know the Opti needs a lot of juice to kick start. So, for me, 3 Optima D34M batteries. Good Luck.96 Eyra/12 Mercury 175 Pro XS with 2015 single axle trailer2017 Victory Gunner