Optimum Gear Ratios?

Having decided that drivetrain speed will be an important design parameter for our strategy this year, we will be using shifting transmissions for the first time in recent history.

We have a few questions.

What seems to be a popular spread for gear ratios? What is a reasonable top speed for high gear? WCP sells transmissions faster than upwards of 20 fps. Is that ridiculously fast? Is a chassis even controllable at that speed? What types of software tricks are out there to make driving at high speed easier?