Five years, $70 million. Drew's decision to opt out of his contract in Los Angeles is looking pretty smart right now.
This is pretty much the going rate for a player of Drew's caliber. Even if it's a bit high, you should overspend for elite players if you're going to overspend, and Drew is, when healthy, an elite player.
However, he's almost never healthy, he's over 30, and he has a rep for being a selfish prima donna. I don't usually say things like this, but I wouldn't be surprised if he struggled in Boston, where he'll have to deal with a very melodramatic and petulant fanbase and media.