Larry Holmes - One of my favourites, would still be a huge factor. Must be pointed out though that his younger streak featured still some weak opponents and the more decent ones like Witherspoon he had severe problems with. He lost to Spinks, that's bad. His best win was as an oldie against Mercer! And Muhammad was shot.

George Foreman - Older version would do better than younger one! Would still be a huge factor because of chin and power and strength.

Muhammad Ali - Would be a factor but only a B-level boxer at HW. Could have got in shape and been a CW champion and served as a sparring partner for genuine HW's

Ken Norton - Would suffer many KO's. Good enough skill but no power and no chin.

Joe Frazier - Would be annihilated, would not even be able to compete

Sonny Liston - Just an oaf. Would not be seriously competitive with the top 20

Floyd Patterson - Would never make it out of the amatuers

Rocky Marciano - Not a HW

Joe Walcott - Would get pulverised

Ezzaard Charles - Not a HW

Joe Louis - Might be able to be a factor at CW but annihilated at HW.

Primo Carnera - would be clowned

Jack Dempsey - Annihilated

and so on...

This is not against Klitschko, this is career performance against a standard run of opponents in the modern era please note!