I've only seen photos from this Olympia before, good find! Have to say that Sergio has Arnie for legs and taper while they are pretty even for most upper body stuff. I think Arnie displayed his physique better though. Pretty sure Arnie won this in a backstage posedown after the judges couldn't pick a winner on stage.
edit: I just realised how that last sentence sounds.
Arnold's amazing and he only got better (bar 1980) but fuck, Sergio's arms just blow you away. Maybe if Arnold had dedicated a bit more time to his triceps he could have had mindblowingly epic arms like Sergio did. Arnold had it much better posing though and also had a better chest (not by much) and was better conditioned.
Legends Of Bodybuilding