Re: Would Ali be as fast as he was if he was active today?
I'm not sure how many of today's heavyweights are bulked up with diet and weight-training, and how many are just naturally bigger anyway. I suppose it must be more a case of the former, as training will have changed since Ali's day.
I think if Ali was boxing in his prime today, he'd still be the same weight naturally as he was in his own day, but he might well gain weight in order to match his modern opponents. If this happened, he may lose a little speed, but I think it would depend on how much weight he put on, and how much of it was muscle.
If he bulked up by around a stone, (14 pounds if you're American) and it was mostly muscle, he may not lose much speed, and would punch harder, but it may just sap his stamina a little?
However, if he went up to about 240-245 pounds like today's heavys, I think he'd likely lose a noteable amount of his speed, though its his stamina which would suffer the most, I think, because that much weight wouldn't suit him.
He'd only be stronger if he gained muscle, but that would be a useless advantage compared to losing his snap.
The truth is, with Ali being like he was back then, he probably wouldn't allow his trainers and criticts talk him into gaining too much weight, due to his sheer self-belief.