Not a big Calzaghe fan here, but I guess he would beat them all. He already beat Kessler in what I still consider Joes best win to this day (Roy and Eubanks were somewhat faded while Hopkins deserved the nod in a close close fight in my book). I can see him outwork Arthur Abraham, and outhustle Carl Froch. Taylor would have his moments, but I can't see Taylor handling Calzaghes pace and he'd fade badly in the championship rounds. Dirrell I consider an easy task for Calzaghe, while Andre Ward is a tricky one - I don't really know what to think about Ward. At any rate, Calzaghe is more tested and far more experienced, so I'm giving him the benefit of the doubt.
Joe wins against all of them. I do see Taylor,Ward and kessler giving him some problems and stealing a handful of rounds, and i see froch possibly stunning him or dropping him at one point. Joe would win UD's against all of them possibly stopping Taylor or Dirrel. He may even stop Abraham through accumulation punching/cuts. I wouldnt be surprised if we saw very,very close fights with Kessler and Ward, or possibly Froch though, there are some amazing fighters in the tournament.
Considering Joe's stamina and workrate is 2 levels above the rest even now, he's the fastest guy out of all of them. Calzaghe wins fairly easily against all but Kessler - and it depends on how much he has slipped for Kessler to have much of a chance anyway.
I think if he fought Kessler again Kessler would win and as for JT i think that would be very close fite....as for the rest he beats them pretty easily