Land speed bike racers have a saying - if it doesn't hurt you're not tucking tight enough. Even without a fairing there is an aero advantage to keeping your head down. Doing the math for that the other day suggested the reduction in frontal area could be worth a mile or two an hour at 100mph. I just bought a new helmet with a taller visor opening so I can tip my head down more and still see down the track. The technique used by a lot of riders is head down for five seconds, look up for a second, head down for five, etc. down the track. This is frowned upon by the officials, but it's also pretty hard to enforce. The bikes are also usually modified to maximize straightline stability, with longer wheelbase and increased rake angle.