DeGale would be a fair deal bigger i'd say but i think Barker's experience and cleverness would mean he'd handle himself really well. Probs would edge it over the course of the session.
Considering DeGale looks confused with both pressure and guys that stand off, he'd looked seriously baffled against Barker.
DeGale still hasn't found his style yet. He wants to be a brawler but he doesn't have the type of attributes to succeed with that style to the very top. He needs to be a bit more like Ward and fight depending on his opponent.