Does it explicitly say you have to practice that scale that way, because ultimately stretching the hand farther than normal slows it down. There is an easier way to play the F major scale. But out of respect for what your asking, it's your call either one will work, speed will eventually grow as you get used to doing it one way. So choose one and stick with it. I generally use index-middle-pinky, just because I can stretch my index to middle farther than ring to pinky.