What weight do you need to be to beat a top super heavyweight with skills?

I think that we need to study the facts on this one.

Alexander Povetkin was the standout heavyweight, outside of the Klitschko family, and he arguably lost to Huck, who was not the best or brightest of the division.

Steve Cunningham was a cruiser weight who never really broke the heavyweight division, and he put the current lineal champion in a fight for his life, and arguably gave him his toughest fight.

David Haye obviously held a belt, and became Wladamir's top challenger.

If you take away the Klitschko's, then the recent crop of cruiser weights, would have done just fine.

The superheavyweigths of the teens/20s did just fine, until Jack Dempsey came along!