Jeff's right, every turn on every race track is going to be different. Unless you have a race car that you can swap gearsets out in for every track, you just need to learn to be flexible with whatever you have.

Autocross courses you can generally count on to rarely get beyond about 60 mph. So, having a 2nd gear that will get you to 65 will eliminate the need to shift to 3rd most of the time.