The short answer to this is a very good one! Even in the warmer months, and despite the fact that the Gulf Stream still reaches up here water temperatures are pretty poor. So you’ll definitely need a 4/3 in the summer.
In the winter though you’ll need some serious rubber, a full steamer with hood boots and gloves is essential, and really by the time we’re into December a 6mm is required for any long sessions. That said with new wettie technology things are a lot better than they used to be.