Man...I'm a huge GGG fan, but the first three are all tough style matchups for GGG (although then again, they were all tough matchups for Toney as well).
I would pick mike to beat him Nunn and Johnson are tough fights that I would expect GGG to win but highly competitive affairs. He should beat Tiberi and Dewitt So for me 2-1 and potentially 4 and 1
Nunn in 1991? I think he outboxes GGG. I remember the one thing James did which to me took the rhythm away from Nunn was when Nunn did his leaning back on the ropes, Toney would lean forward and nail him in a very unorthodox way. GGG wouldn't do that and Nunn would be able to take him to the ropes and avoid big punches like he did against Barkley. So the ropes were not going to be effective for Nunn, and the right was landing for Toney in the center of the ring. At the end of the fight he put the left hook together. Mike? Hell of a fight. Draw maybe ? I really don't know. I tell youone thing. GGG would not stop McCallum who fought Toney in Dec. of 1991. Johnson? I pick GGG to win a decision. Tiberi. GGG wins by knockout. Dewitt. When Toney fought him in 1992 which I think was his last fight? Or the Dewitt who fought Hearns in 1986? The 1986 Dewitt I think losses a decision, but Doug had a nice counter left hook and decent left to the body. It would have been interesting. Which Nunn are we talking. The Nunn of 1988 I think embarrasses GGG.
we can divide them into elite and non elite, since we know 3G can beat non elite but cannot YET beat elite. So - non elite - Tiberi tiberi was not a top contender so he might stop him, based on g stopping several less than top contender. Dewitt - doug was a former 3 time champ so this might be tight, it would be tight SD, very marginal. It might go other way. A leve lof opponent somewhere between canelo and jacobs. Johnson - not sure 3G likely beats these guys except not sure about Johnson. might be either way if he is on form and he is quite big, his top wins trump anything G has done by a large margin. elite - Nunn McCallum 3G may draw with one and lose to one, based on his actual what he did. so at best 3-1-2 in the middle 3-3 at worst 2-4
I'd pick him fairly confidently over all of them except maybe Nunn. He'd have to degrade Nunn over time and try to put on the pressure in the late rounds, more or less as Toney did.
I think he loses to Nunn and Mike Mc Callum. The Johnson fight could go either way. GGG would outpoint Tiberi and Dewitt