Just got back from Coz, and my wife and I were both content with our 5 mm full suits. Oh, we could have gotten away with less neoprene, as there were only a couple of moments when we were glad we had erred on the side of more rather than less--some clouds/drizzle on one day, and another time at the end of a lazy 80 minute dive. When I'm just drifting along for much of the dive and hardly working my muscles at all--not atypical for Coz drift dives--I do feel the effect of gradually losing body heat. That said, on a dive when we find ourselves fighting a current for a few minutes, I may feel warm and let a little water into the neck. In any event, my thinking is err on the side of too much rather than too little. I HATE feeling chilly. I'll continue to bring the 5 mm on Coz trips in the shoulder season.
