The maximum I've seen is a little over 0.7 for acceleration and a little over 1.1 for breaking - slamming the anchors on from 180mph plus gives some really impressive values!
But you are correct, particularly for acceleration, the peak values will have been much higher, it's difficult to maintain acceleration for a 2 second period whereas prolonged deceleration is easier to achieve. You will only be able to achieve the maximum values if you happen to start accelerating just before the 2 second interval starts so you can maintain it over the full period.
