Yes, sure: this is a very well researched set of lines with a lot of information online both here and over at rootsweb msg board too. It's a huge amount of information but in a nutshell it goes like this (others can correct me if I"m mistaken; this is from memory):
Two Usher brothers sailed over from London in the mid-1630s to Boston, Robert and Hezekiah Usher. I believe Dunstable Mass bespeaks the Robert Usher line, as Hezekiah stayed in Boston. Both were notable citizens, especially Hezekiah, who was in the bookselling trade; Robert was a farmer (his will is somewhere on the Web, as is Hezekiah's). Your mention of a relative b. 1639 would probably be a son of Robert's, therefore.
Research on these lines has been going on for many decades, and there's a lot! I will try to return with a handful of good links to start with, and others can help you too. As for the connection with England, no, it is not yet proven, and remains the grail of the Usher researchers; but a couple of years ago an Usher family in England put info. online that does help, and suggests that a Samuel Usher in London was the father to Hezekiah and Robert Usher.
From the other end, the trail starts in the late 1300s in Featherstone in the West Ridings of Yorkshire and goes on without a break to Samuel's generation in London. Most of us are happy just to have so much information, but even though professional researchers have been hired in England to establish the connection to Boston for sure, it remains unproven, for those happier with absolute proof.
Certain among the rest of us skip that clouded bit and romp on back before Jacobus Usher in the late 1300s in Featherstone Castle to where he might have come from, and soon run into the fact that Usher was the name of a job under English kings, and that our family name began under King John when he was in Ireland for a man whose name otherwise was de Neville; and that spills open a great cornucopia of history as the Neville family still are royals and go back and back, if you care to (why not: it's fun), even to Charles Martel routing the Moors from Spain in, what was it? the 8th century.
Well, you can at least be completely assured you descend from one of the two brothers, and it sounds like it's Robert. The rest is just our form of winter entertainment, though secretly we believe it.
Will return this weekend with some hopefully helpful links, or others can provide them too. There are many!