In my experience, Boston to Providence is pretty fast and pleasant. The issue is the rest of the way to NYC, which crawls through Connecticut at a snail's pace and takes something like 3.5 hours. It's a pretty brutal trip.
From New London Connecticut to New York City Penn station its average time is 2.5 hours. I live in New London and I have taken this route a few times for job interviews in New York.
New London is pretty close to the Road Island boarder, I don't think 3.5 hours is accurate, at least not on average.
I code on the train and it's by far my favorite type of travel, so much room and WIFI included with ticket. It's awesome.
For perspective, it takes 2.5 hours to drive on I95 from New London to New York. If you take a train you don't have to worry about traffic, or parking, or pay attention to the road.
It's great, I just wish the ticket price was a bit lower.