Obviously your best chance for this is 1: 6 to 1: 20, since it's the line up with the easiest runs, the hardest for me being 1:15 - Cross-Section, 1:19 Approximations and 1:20- Torque. A few tips.
Number one: Take it SLOW. It doesn't matter how good you are, overconfidence will screw you over here if you don't pace yourself, especially on the aforementioned levels.
Number two: The right trigger is your best friend here, moreso than the brakes. On levels like 1: 17- Stairway to Heaven and Approximations, there's no point using just the brakes otherwise you won't be fast enough to level the track out.
Number three: If you're failing like mad and you're getting mad yourself, just leave it for a day or so or you will never be able to do it.
Good luck.