Two or Four? The new HPDI two's are nice and the actual useable HP is much better on a 2 for what it is rated. A 2 150 will run circles around a 4 150. 4's much better fuel mileage but more money. I would go up to a 150 if it will fit or as big as it will take up to a 150. As soon as you go over 150 the fuel consumption is much more noticeable. A 135 is a good option on a 19, and should push it around 38-40 with gear and two people. A 115 will push it about 33 with a stainless prop and two less with aluminum. Add 4-5 mph with a 2 of over a 4 with same hp. A 150 will push it 50. As long as you can cruise at best fuel mileage around 35 you are in the right HP range for max speed/power fuel use. Either a Honda, Yamaha, or Merc are all excellent.