Spareparts, the "60 plus club" welcomes your enthusiasm.
The 150 will do most anything the V was designed for. As for the most ponies in an outboard, I have heard of a guy with a 260 Merc 2.5L that made the boat scream. A few have the new HO E-tec 200 which is really near 235. Several sleepers with modded v-6 Johnnys or 225 Yammy hiding under 150 cowl. I am stuck on 250hp. I have the need for speed. Weight is a factor as is fuel consumption as MJ pointed out. The condition of the transom is a huge factor. If the transom is just marginal a big heavy motor may decide to finish it off, where a lighter 150 would work well for years to come.
UBHSTRY on here has put a 400+ hp (guessing) Stroker V-8 SBC in a I/O cuddy and has plain blasted past the 65 MPH mark.