Over the years I’ve stopped a number of people jumping in with their cold water weights.snip...
During one of our invasions, we had a ScubaBoarder, that was not a part of our group die there in the Keys. She was a Cold Water Barbarian, where she dove a dry suit and an aluminum tank. Down here, the dive op provided her with a steel tank and she wore a bikini. They asked about her amount of lead, but she told them she really needed that weight. She died in thirty foot of water with her 26 pounds of weight still on, a full tank and her reg out of her mouth.
The warm to cold tends to be less fatal. But I have seen, only once, a 3mm shorty in a quarry during February; they lasted 10 minutes.