Hi Fred S. Welcome to ClassicParker! You will likely hear good reasons to support all three of the options you mentioned. Here's my 2-Cents. We have a 2013/2014 2520 XLD with a single 2014 Yamaha 300. It has topped out at 44 mph with low gear/weight. Its 'sweet-spot' is cruising between 30-32 mph, getting 2.0- 2.2 mpg. (Ave. 4200-4300 rpm)... I hold 200 gallons of gas. (does not have that EPA contraption). 14 gallons of fresh water. Two coolers and average extra gear. Usually one-three people onboard. For us, the 300 has been adequate, and I prefer to maintain only one engine. Installing two 150's adds weight and there is no more power; if you want twins, go with twin 200's, but there's still a diminishing 'rate-of-return' with the extra weight of the second engine. The argument for the 'safety' factor of two engines is not one I totally disagree with, but countless commercial offshore boats have one, well-maintained engine... Many (most?) 'engine' problems are fuel-related; both engines draw from the same fuel tank. If the fuel is bad, it's bad for both engines. With that said, I do understand the psychological comfort of having a 'get-home' engine if running far offshore, as long as a problem is not fuel-related...