If you are buying a used boat, obviously the power installed is the power you will get if you buy the boat. But for new boats, request a demo boat with the same make and model engines as those on the boat you are considering. This is important because, for example, you may cruise with a crew of four or more, keep the tanks full, and have a bunch of gear stowed aboard. Conversely, sea-trial boats are typically lightly loaded and sparsely crewed. So the weight disparity between trial boat and actual boat can result in a performance deficit on delivery day. Bottom line? If the boat performs sluggishly during a sea trial, you may want to order the boat with more power. Also, consider that the differences between power choices may manifest themselves in the form of serviceability or stowage capacity, not just speed, ride, economy and handling.