Wow! Great matchup. Zarate the banger against Castillo the counter-puncher. Castillo counter-punched a great banger like Jesus Pimental into knots and went 44 rounds with all-time great puncher Ruben Olivares and didn't taste canvas. Zarate would actually have to box Castillo and I think he would. Zarate was far more than just a banger, but that is what he is known for. If he didn't plan on boxing and utilizing his height and reach, his plan would change with the first counter that buzzed him. I go with Zarate over 15 rounds on a decision.
I think that the results would have been the same as Castillo-Rose and Castillo-Olivares....a 15 round decision win for Zarate, with Castillo performing just as valiantly and smartly as those two fights, being the tough, clever guy that he was and even sending Zarate to the deck possibly for a 2 count. I think Chucho would have stayed on his feet throughout and avoided a kd.