I'm in the same boat as you. Both are phenomenal at ruining other's gameplans and rhythms. Both very different stylistically though.
I think it'd be a bloodbath personally, both have good defences, but both will be taking some serious punches here.
Wierd fight to imagine. I can't picture the fight in my head, so I went with the better fighter - Monzon. I doubt he'd stop Joe though, and I reckon it would be close. Monzon is a ******* head to head.
Important point; Monzon was 160 on the day of the fight, Calzaghe is 168 the DAY BEFORE. I think there'd be a fair difference in poundage on fight night.
I favor Monzon here, for the close decision. I think Calzaghe might taste the canvas for the first time in this fight; but I also think he gets up and finishes the fight (while making it close). I think that Monzons awkward style and ability to throw people out of their normal routine would show against Joe, who is used to doing that himself. I also think Monzons effective jab would keep Joe at bay until he lands a perfectly timed right hand or two and stun Joe, or like I said send him to the canvas for the first time. Monzon surely wasn't as quick as Joe but he had excellent timing and I think that he would negate Joe's workrate and land more solid punches. Question: is this fight 12 or 15 rounds?