Calzaghe is a good fighter for the "modern" times (12 round championships). In fact... I love the guy and root for him always. However, I don't see him in the same ring as the Marvelous Marvin of the late seventies or even the mid eighties. Marvin fought many "big" middleweights in his carreer and obviously handled them well. JC would have needed to come down to 160. There was no negotiations from the Petronelli's to that end and they would have made JC dry out for a same day weigh in. In my opinion Tommy Hearns (at 16 would have gotten to Mr. Joe in eight, nine or ten rounds Roy Jones in his prime just before moving up to light heavy weight would have made him look silly for 12 rounds.
Just my opinion...