Hi Aegir,
As a newbie diver, I don't know that my opinion will mean much, but I just got back from Grand Cayman a month ago, and the water temp was 79. All I used was a lycra skin, and only once did I even think about the water being a little cool.
I think it will depend on whether you have a tendency to get cold or not, but I would think the a 3/2 would be plenty to stay warm with. If you tend to be warm anyway, then maybe something less, so you have better mobility? But, as a person who hates to be cold, I would say more is better.
dmentia