I just tried imagining a young Calzaghe in with Froch and I think he stops him, Calzaghe did hit hard, even Eubank admitted that.
If Joe had seen the slightest bit of reaction from Froch to any of his punches then Joe would be on him like thresher shark;D
Even if Joe now wouldnt have had the power to put Carl down but Carl did that daft stumble and pirrouet in to the ropes Joe would have poured it on and Carl wouldnt have got out of the 3rd.