where are you getting your info?? Take a look at the manga page, where Hiashi gets a brief one-liner. "Do not forget; the Hyuuga are the strongest in the Leaf."

Speed is completely based on how hard the individual ninja trains. It's in muscle strength in the legs and quick reflexes, which the Hyuuga have proved themselves to have. I mean, to time the Kaiten, you have to start it JUST BEFORE the incoming projecticles hit you, not a second too late or your screwed.