Positive responses to each of the following questions define the answer. Sailing upwind in the prevailing light air, most of the boats in the rally had to crank up their diesels to keep up with us. Speed is desirable when cruising, simply because going from point A to B under sail is what it's all about. But if you have to crank up the engine, even when there is breeze, to make a decent day's run, you are on a slow powerboat that happens to have sails-in my opinion.
Length is most important.
Average speed in knots for the typical sailboat is roughly equivalent to the square root of its waterline length. True performance-cruisers most often have fin keels and spade rudders. Reduced drag means the boat does not need as much sail or as large a rig to achieve speed under sail, and upwind efficiency means faster passages. More sail requires heavier deck hardware for the higher rig loads and more hands on deck in heavy weather-just what cruisers don't want. Because such a boat tends to have a high center of gravity, good speed can be achieved only by placing crew weight or movable ballast, such as water, to windward to reduce heel.