In Northern MA and NH water temps are:
60s- Late june/July
70s- every 20 years or so.
I start wearing my 4/3 with a 3/2 hooded vest around mid-April although now that I have a 6/5 I might just wear that until I can go 4/3 with no hood which would be sometime in May. Gloves until mid may, Boots until June. Im not a tough guy and enjoy being warm. I prefer to wear warm gear and stay out for 4-5 hours than go light and start to get cold in an hour.