It's all speculation because Charles didn't face a lot of big boys outside of Valdez, who beat him. That was after his title reign, and I have made the argument that Charles would have won had there been a rematch, but the fact is that there isn't a lot of data. I feel that he would have beaten all those guys, but can't offer a lot of data--just personal perception.
Charles during his title reign definitely has a very good chance at going undefeated against this lineup. The two biggest threats would most likely be Spencer and Shavers, who are the most unpredictable of the group.
He beat Joe Baksi and Elmer Ray off the top of my head. Two guys who were over 6 feet tall and 200 pounds.
Charles was a fantastic ATG pound for pound fighter, but his worst weight was heavyweight. Looking at his career at heavyweight I'd say somebody on this list would beat him.
5-0, the possibility of Lyle or Shavers landing a big shot is there but his skills were so vastly beyond theirs even at heavyweight, both of them might have trouble finding him in the ring to land a big shot.