The problem is there aren't any pitchers available who are even remotely close to his value on the free agent market in 2014. Garza, Johnson, Burnett, Hughes and Feldman won't be able to fill his innings. If the Red Sox trade for a pitcher, they hurt their future by trading away pitching prospects. I doubt they make the playoffs in 2014 without him.
Its a no-win situation. Signing him 6+ years will end up being a mistake, but trading him before 2014 will also hurt the team. Maybe waiting till the 2014 deadline makes the most sense-- a desperate NL team might be willing to give two top 100s for him.