I doubt that Manny would have Wlad go for the KO...I can see Wlad dancing around George for 10-12 rounds.

Big George would have a time with Valuev but since Nikky can't move so fast i say George drops his ass in 6

Sergei has a decent chin on him Foreman could earn a UD though

Maskaev would brawl with George which is a "no no" for anyone until George is like 80

Young Foreman would be champ in about any era ever