Calzaghe would have been in trouble then. He was a power puncher until at least 2000. His hands screwed up and he changed his style and, frankly, became a better fighter as a result. Collins' jaw would have survived Calzaghe's then good, but probably not excellent, world championship level power and it would have been close on points. Calzaghe is an example of why this 'prime' thing is slightly redundant. The youthful Calzaghe power puncher would not even beat the Calzaghe of today. I always think of Tszyu when it's said he was past his prime vs hatton. now maybe he was a little too old at that time, but I would always say the later Tszyu with his accurate, better choice punching was more of a nightmare for Hatton than the more athletic but more frantic earlier Tszyu. However, the versions I consider to be Calzaghe and Collins' peaks (vs Lacy for the former and Eubank 2 for the latter), I'd take JC to win on comfortable ud.
It's interesting that like with Mac-Nelson, he picked the fight when the champ was old, and in both cases the champ ended up leaving the title behind. Do we blame the champ for bowing out for whatever reason, or how about the challenger for waiting till thew champ is oooollllldddd? My belief is that the fight was made only because of Collins-Cummings! Collins WAS on better form than Eubank, let's not forget, and Joe had some problems in there with Eubank who had probably trained some knock out an easy opponent at 175.