Looking at both fighters, I was a fan of both. Regarding McGuigan, I totally loved his style. Such a strong and hard-punching featherweight, with reflexes and workrate to match. A fight with Azumah was one I wanted to see so bad. I know I am in the minority here, but I would have picked Barry on that one, but admittedly, maybe I'm picking by heart rather than head. As for Olivares, we all know of him as one of the greats at 118, but I always believe he was so underrated at 126. Of course, why he is underrated is his own doing, as he was in party-mode by the time he moved to feather. He would whip himself into immaculate condition for a fight that mattered, but against someone he took for granted, he wouldn't train and looked like crap in the process. Those that took advantage of this was Art Hafey, David Kotey and Carlos Mendoza. The Hafey fights in particular were a remarkable contrast with each other. Coming off the fantastic first performance against Chacon, he shows up ill-trained for this kid from Canada that nobody knows about and gets blown away in 5 rounds. In the rematch, he is dead serious and produces an absolutely brilliant performance of matador-like boxing. So narrowing these two fighters to lab-like performances at the height of their featherweight powers, I would go with Olivares over McGuigan on a very exciting 15 round decision.
I get where your coming from with McGuigan v Nelson. Most now would give it to Nelson easily, but back before Barry lost he was looking excellent and still very young ,so seen as having a great chance to win. As for Ruben ,if we put his best performance at Feather up against Barry's then yes,would have to go for the Mexican .A bitterly ,hard fought fight with both men right in the thick of it .I can even see both men down at some point but neither stopping down. Barry would lose on points but it would warrant a rematch .