Hi, Dom! Welcome to ATP. New England ... well, mountains will make it much colder and extremes more extreme. Coasts and lakeshores will be warmer, or at least less variable. Speaking very loosely, Rhode Island to Maine, anywhere from Zone 3 to Zone 7. (For Zone 3 to 7, that's -40F to 10F.)
Another way of saying "USDA Hardiness Zone" is "what's the coldest is it likely to get next winter, where you live?".
It's important to remember that the USDA Hardiness Zones are AVERAGES.
For example, my Zone is 8B, therefore about half of my winters stay above 15-20 F. So far, so good.
However, that means that about half of my winters dip BELOW 15-20 F at some point. Plants that are only marginally hardy for my zone should only die in HALF of the winters!
Of course, the direction that a bed faces, shade, wind, rain and snow cover all affect the actual temperatures that each bed actually experiences ("micro-climate").
And I think that there is a HUGE random factor that comes from how steady and consistent the changes are during spring and fall. Plants like gradual transitions and no unexpected reverses. Ideal weather would be gradual cooling over fall, consistent cold under snow cover all winter, then a steady warm-up in Spring.
An "Indian Summer" can "confuse" a plant and cause it to put on late, tender growth at the wrong time, which then dies back when fall finally gets around to chilling down. A late cold snap in Spring can kill plants that "did the right thing" by putting out lush spring growth at a date when they "expected" settled warmish weather.
You can squint at maps down to street level, and debate whether to use the very latest USDA updates, and resolve to grow only plants hardy to two full zones colder than your "official zone", but the weather next year is going to do whatever it does, and the plants will live or die based more on micro-climate, actual hourly weather and their general health more than a comparison between a statistic and a label.
As Greene said, plants don't read zone maps!
Persoanlly, I think plants delight in fooling us. Plants that "should" thrive, die year after year. Plants that you expect to love the climate, die as soon as you turn your back after planting out.
When I'm especially desirous that something survive, I always talk around it like "Oh, I don't think THIS one will make it! The odds are really bad." The only better way to stimulate a plant to be hardy is to uproot it crudely and throw it on the compost heap, then ignore it for two months. THEN it will thrive, just to mess with our heads!
P.S. People who sell plants commercially sometimes fib about how well adapted a plant is to their region. Big box stores especially sell anything that brings in cash. If all the plants you bought this year die, that makes you a customer again next year!