It's possible to KO anyone, but in his prime between a solid chin, excellent defense and the willingness to spoil any which way, it's hard to picture many middleweights doing it. Hearns and McClellan maybe, if they could break through the guard and movement and hit with the right punches. Generally, I wouldn't favor a KO win over Hopkins until we start getting into light heavyweights, where there are a couple of guys like Bob Foster that could certainly pull it off.
Dawson isn't very good though.Never bet on mediocrity to get the job done, even if Hopkins is older than god at this point.
At mw? Possible but very unlikely. His combination of defense, chin and survual skills is just too good. At lhw on the other hand there are quite a few who could do the trick. Charles, Moore, Foster and Spinks would be my picks. Others like Tunney and Jones have a good change. My wildhorse pick would be Paul Berlenbach. You clearly are a gent and a scholar. :thumbsup