Obviously not the case all the time but give me some modern examples of fighters who fit the description. On a side note, Do you think Yuriorkis Gamboa will be one of those fighters?
Calzaghe = Full Speed + No Power Forearm = No Speed + Full Power you can certainly have one without the other
Calzaghe was a puncher in his younger days before his hands become so brittle. He admitted later on in his career that he protects his hands in fights and doesn't punch with full force unless he feels he really needs to(eg to earn a fighter, respect, like when he stepped it up against Kessler).
A fighter that has one punch ko power (that falls into my category of great power) does not have great speed because they have to sit longer on the punches; however, you can have decent power and great speed or vice versa and yield great results. For example, Shane Mosley (Great speed decent power) Mike Tyson (Great Power decent speed)
Its simple mechanics really, you need speed and strength to ko someone. Sometimes punchers look slow when unloading because they need more time to transfer their body weight into a shot. I'd say david haye is an example of a p4p hitter currently has both speed and power. The strength element comes in as you need this to 'follow through' with punches to really rock an object.
I would say Mosley has better than decent power, in his at LW he had Great Speed and Power, and Tyson at his peak was very fast.
Tyson said it was speed and accuracy that created power. He got that from Cus D'amato. Obviously it'd be more important to have BOTH but I think if you're fast enough and you have decent power, you can pretty much create your own KOs.
Speed kills period. Anybody who has ever been in a ring knows it. If you get hit with a punch you don't see, it feels 10X more powerful than it actually is. Ask some of Mayweather's opponents.