I can see Holyfield and Lewis being difficult for pretty much any all time great champion....Wlad wouldn't necessarily be a cake walk for Lewis given Lennox's propensity for starting slowly and unenthusiasticly.

As for Bowe I'm not so sure. To me he had great potential but other than Holyfield and Golota he never really tested himself vs the best of his era (namely Tyson and Lewis) and if Golota worked him over then I figure Wladimir could do even better.