A 3mm in 29c water yesterday, as snug as a bug in a rug, did not overheat suiting up in 30c Bali.
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What data do you have demonstrating that avoiding a very minor bit of feeling slightly cold, and only at the start of the dive, makes a "significantly" longer dive time possible. My experience is that it makes almost no difference, and that physical activity is the main factor, other than depth, in establishing dive time, all other things being equal. You may doubt, but heavy suits are constricting, require more lead, and detract from the experience. Except for stinging and rash, no suit at all is the most pleasurable.
If I want a sensual experience, I'll do a midnight skinny