Joe's movement and fast combinations would give GGG hell in my opinion. His size and strength may very well too, isn't Joe naturally a quite a bit bigger?
GGG is an averaged sized middleweight. 160 is the perfect weight for him. GGG is one of my favorite current fighters. His one deficiency is an occasional porous defense. I believe JC wins 9 rounds to 3.
Considering we don't know how good GGG truly is as he hasn't fought an elite fighter yet and he is an average sized MW, who is talking of fighting Floyd at LMW, I would have to go with Calzaghe. Calzaghe had a great chin. I know he got dropped a couple of times late on in his career, but Joe could take a shot. We also have to remember that GGG is hittable and no one has ever made him fight at a pace or a range that he isn't comfortable with. Joe would do both of these things to him. At this stage of GGG's career I would have to give him only a punchers chance against JC.
We havent seen how effective GGG would be at 168 but going from what I know now id favour Calzaghe/Froch over GGG Calzaghes work rate and ability to adapt would get joe the victory over 12 Froch with his power, iron chin and relentlessness would wear GGG down Ward (whilst beating Froch) just doesnt have the workrate to bother GGG and Clinching against this guy is a deathwish. You fight on the inside and you will get knocked out
Calzaghe wins comfotably, and then we all start saying GGG wasnt really that good as his best win as yet is Murray.
GGG is at his best at mid-rang and long range. Pushing the guy back to take the sting out of his shots, not letting him dictate the pace of the fight and tying him up could be a good tactic. It would take ***** to do it though as any sane persons natural reaction to power like GGG's is to run away.
I don't want to pick against Calzaghe, but he wasn't the world's hardest puncher, was he? I think that anybody without the power to keep GGG honest, has problems with him. Can't really pick this one, beyond saying that the dragon was much more proven.