A standard halogen should get around 20 lumens/watt.
L&M's HID gets about 675 lumens at 13.5 watts.
That means that your 30 watt halogen light's making 600 lumens. If you can only safely travel at 13mph on 600 lumens, 675 isn't going to get you any more.
Anyway, to find the distance to reaction time and speed, distance=mph*1.46*reaction time.
So for a 2.5 sec reaction time, you need to be able to shine a light about 65ft.