McCallum was greater, but I think the 88-89 Nunn wins this. Nunn had the style, and the tools to defeat McCallum. I can't help but remember that Kalambay schooled McCallum in their first fight, and Herol Graham, a far inferior southpaw to Nunn, pushed McCallum close. Nunn never again hit the same stride after he destroyed Kalambay, but at his Tate fight best, I think he outboxes McCallum.
I thought McCallum easily beat Graham. All Graham did was run around and hold. And while McCallum is careful to give Kalambay credit for his win, it is true that McCallum arrived in Europe only four days prior to the fight and claims he was highly jet lagged for that fight.