I'm ok with giving him 6/100 for many of the reasons others have posted already... weight issues aside, he's still relatively young (28), plays a premium position of need for the Sox, plays it well defensively, hits for power and average consistently, ability to switch hit, and can easily transition to DH/1B once Papi is done.
And it's not as if the 6/100 contract would be that large of an albatross for the Sox to overcome if he ended up becoming a dud for us in 3-4 years either, considering the resources ownership has at their disposal. They can easily afford him and not worry if things don't go as planned.