I've found the advice given in Atlantic Kayak Tours Expert Center to be very helpful. AKT gives clothing suggestions for various temperatures. With they current 50 degree water temps, they agree with Russ: dry suit. Other outfitters are a bit more liberal, for example, Empire Kayaks permits 3mm wetsuits or dry suits on their seal watch paddles usually conducted in January.
This mild winter, I got my money's worth out of my dry suit being able to paddle all year round. I like warmer weather before I can feel comfortable in a clammy wet suit. But then, I tend to be the last person out of wet & dry suits in the spring, and the first person in them in the fall.
Lots of good info on several different paddling topics on AKT's Expert