Speed potential is more sail area, waterline length, lighter vessel, rather than beam, other than the fact that when you heel over the beam will increase waterline length for certain vessels. I believe S-2 is considered to be a better built boat than the Islander, with better fiberglass work, but, as mentioned, the Islander 36 is a very well respected vessel with lots of experience on the water. I have just seen S-2's hold up better with time. A center cockpit boat usually does not sail as well as an aft cockpit boat because of the sail plan difference, more weight and windage. But, they can be more comfortable for cruising and most offer a great fishing platform aft where you do not have to bring fish guts into the living area of your aft cockpit. That's my 2 cents.