When he dose get hit flush he reacts pretty well. At the very least we know he dose not have a glass chin
Hook knocked him off balance and forced an uncalled touch down with the glove. It still remains the one time in Floyd;s career where he was down as a result of a punch. Judah hits hard and fast enough where there's no real shame in suffering that fate, and May went on to dominate a short while after tha, which usually happens after he gets stunned. So his recuperative powers are fine, and his chin is decent, at any rate.
Manny hasn't had a stoppage since 2009. He hits hard but its usually the fact that the combo of speed and his opponents not seeing the punches are what get him knockdowns.
Floyd has the most overrated chin in modern boxing history. The guy's defence is so good he hardly ever takes a flush, hard shot. And it's a good thing for him, because whenever he does take one (Corley, Mosley) his spaghetti legs are all over the place.