"My thinking is to aim for being a little too warm, and let in some water if that happens. If I had to choose between being too cold or too warm I would choose too warm.
"
Same here, always. I can cool off a lot easier than I can warm up.
Funny story: I was on a Bahamas trip once in October when--as usual--I was the only diver on the boat who was using a dry suit. There was the usual, thoroughly good-spirited ribbing from the wetsuit divers. The water temp was harder to handle than everyone expected, and everyone was getting cooler by the day. I have a photo of one of the DMs hovering with her arms wrapped around herself, trying to conserve heat. By mid-week, one of the other divers jokingly said, "I'll give you $2000 for your dry suit."
That was a sweet moment. Usually the one most prone to hypothermia, I was the only diver who was comfortable all week.