toughest middleweights ever

What about Stanley Ketchel. Another Middleweight who fought Light Heavyweights and Heavyweight. Two time Middleweight champion. Almost beat Philadelphia Jack O'Brien the then reigning Light Heavyweight Champion and went twelve rounds with the great Jack Johnson and put him down, how many did that with a prime Johnson? He went six rounds with Sam Langford, lost the decision but some thought Ketchel had won. He was tough, possibly the toughest!