1984-1988. Sean Mannion - Sumbu Kalmbay 1. It's been a long time since I watched Himenez, Valejo, Suero fights though. Mccallum was pre-prime against Kalule.
i think he was at his best in his 30's, he was never very athletic, and as he aged, he only became smarter. similar in this way to hopkins, moore, martinez ie fighters who improve with age (ie experience)
He was at his absolute best at junior middleweight, from the early 80s through 1987. Once he moved up in weight he was still an excellent fighter, but not quite as good.
I'd extend his prime to include the Graham fight, but more or less what lester said. I don't believe moving up took anything away from him per se, you would have to be a sorry fighter or purely relying on size against blown up Welters to be significantly affected by a 154 to 160 transition.He was just getting past his peak physically soon after it and fighting better fighters back to back than he had been at 154.He was always a middleweight physically anyway, huge at 154.