I've been diving a 3/2mm for the past two months and think 63 F is quite comfie for a dive or two a day (even with bottom temps of 57 F)... but then I have accumulated sufficient bioprene to keep me warm as well. I'm always amused when I read of Florida divers who do not dive year round because it gets too cold! Sheez... try 47 F in a wetsuit (7 mm of course) here. I have a dry suit but it is wetter than my wettest wet suit and therefore I've only used it once. Of course those with less bioprene may get different mileage!