Apparently MT is at 520 feet and will be 60 stories (but still the previously discussed 685 ft)
At 520 feet above downtown Boston, the upper reaches of the Millennium Tower are open to the sky, a few fingers of steel girders and temporary fencing framing workers spreading concrete for each new floor — a third of an acre every other day.
http://www.bostonglobe.com/business...wn-crossing/AiK6LiMxSmiwKIbb837uHN/story.html
This number is wrong. It's absolutely higher than 520'. The writer made the mistake of thinking it's 60 actual stories, and not just 60 "labeled" stories. Basing his calculation off this, he simply did 50/60 * 685 = 520.83333.
If we base it off the expected 56 actual stories to hit 625', and allow that the podium floors offset the high ceilings at the top, we get 50/56 * 625' = 558'.
I ask you to draw your attention to the picture below, taken from Woburn, about 9-10 miles out. (distance helps to "flatten" perspectives) Note 1 Beacon, just to the left of MT, which stands at 507', and is at a higher elevation than MT. I believe it's also technically closer to the camera in this picture than MT. You can see that MT is clearly pushing 3-4 stories beyond 1 Beacon at this point, even with 1 Beacon at the top of a hill.