It all depends, 50 degree water is usually means that the air temp is pretty chilly especially if there is a north wind. If you want to be warm and surf for at least a couple of hours I would recommend a 5/4 or 4/3 like the administrator said. Booties and gloves will definetly keep the extremeties warm as well, because those are the first body parts to get cold. If money is an issue I would go with the warmer suit, you will get more mileage and comfort out of it. Just my 2 cent!