A big issue for cold water diving, is choosing the right combination of gear.....While you might "get away" with a thick wet suit for Shallow dives, matched to a very heavy 120 or 130 cu foot tank and maybe even more weight....this is only "ok" for shallow.....not really OK...it just wont by itself be catastrophic. In deep water, the thick wetsuit loses bouyancy, and then the heavy tank is a real problem. This is why a dry suit is a much better solution for cold water diving, than is a thick wetsuit....that and the dry suit is much warmer
With the dry suit, you don't have the huge buoyancy shift that occurs with a thick wet suit as you go deeper, and all the major buoyancy and trim issues this will create for the diver. Also, a 30 pound wing is all the lift you would ever want for this...On the other hand, we hear about divers in cold water that don't want to spend the money on a dry suit, and who got some "deal" on a thick wetsuit. They typically are then talked into very heavy monster tanks like a 120 or 130, and then plenty of weight on their belt in addition....This diver is then even further screwed up, by being sold a huge monster wing or BC that could lift a sunken boat....they decide they need this if they get deep, and lose the buoyancy of the suit to depth, finding themselves horrendously overweighted. This results in a high drag, slow moving diver, that sucks a lot of air because of all the work they have to do moving the huge BC around. With all the weight imbalances, many divers like this find it almost impossible to swim horizontal ( slick way to move through the water), and end up swimming head up, feet down in more of a 45 degree angle--pushing a huge bow wave. They go even slower from this, and use up even more air with the extra work. Then they are talked into double 120's or double 130's, because they just don't get enough bottom time. Then they have to buy a doubles wing or BC, along with another regulator and the manifold for the 2 larger tanks they just bought. With all of this new kit on, they are even slower, working harder, and diving becomes less fun. Suddenly Golf looks like a fun pastime, and the dive gear is up for sale.
Dont go the thick wetsuit route and end up playing Golf......Buy the bp/wing with the 30 pound wing, a drysuit, and either an al 80 or a 100 cu foot single tank. We talk about diving here on scubaboard, not golf