Canadians may have more tolerance to cold than me, but when I was in Coz in early December, my buddies and I initially dove with 3/2 full suits, and on cool/rainy/cloudy/windy days (of which we had several) we really got chilled by the end of the dive and were shivering back on the boat. After a couple of days of being uncomfortable, I switched to a 5/4 and was much happier. I think it's not just the water temperature; the weather makes a difference. If I exit the water already cold, it's harder for me to warm up during the surface interval when the weather is cool/rainy/cloudy/windy.