I don't know... There have been heavies you could hit with anything but the kitchen sink and you stil couldn't knock them out (think Ali, McCall etc). I don't know how strong Vit's chin actually is but the fact that he's never been down while fighting a few really huge punchers could put him in the same list.
i doubt tyson wud hav knocked out vitali id go with marciano or foreman, tysons punches came from great speed and his ability to put his bodyweight into his punches but marciano and foreman had that destructive knok u into next week power
i think tyson and marciano would have trouble with Vitali because Vitali knows how to use his height. To ko him (not the tko from the cut) you would need a bigger guy like Lewis. I think Valuev would be able to land harder punches on Klitschko because he wouldn't be punching so far down, but he wouldn't be able to ko him ;cuz Vitali would be too busy beating the snot out of valuev.