Steele was a bit like a Tommy Hearns IMO. Good, talented boxer with big punching power, but perhaps a wee bit susceptible to power and pressure himself. Whatever the stories about Steele's supposed injury, it seems to me that he was reluctant even beforehand to fight Apostoli a second time, and eventually gave in to the pressure to fight him if he didn't have to put his title on the line. And of course he gave up a piece of his title rather than gave him a title shot after their rematch. It seems to me that Apostoli must've given him a rough time in their first fight, and Steele must've sensed that he could not beat an improved and more experienced Apostoli. And of course, after the beating he took from Apostoli (whatever the exact reason), Steele was never the same fighter.
Based on that, I give the edge to Zale in this one, in a fight that bears resemblance to Steele's loss to Apostoli. Steele gets off to an early lead, but I think the strength and pressure of Zale gets to him late and does him in.