I have grown up diving the cold waters of the NW Oregon and Washington. I have dove in as cold as 34 degs. I have always dove a wetsuit. Here the popular thing is a 7mm farmer john. I now dive a Bare artic 7mm full suit with a 5mm hooded jacket. Last time I was at Hoods Canal it was 44 degs at depth and I unzipped my hood about 2 inches to let a little cool water in. I did my rescue class in 49 deg water in only my 7mm and without a hood most of the time. BUT... everyone is different!! In the same class people in much heavier suits froze.