The reason you want to change AFTER the torque curves cross is:
You start slowing down the instant you disconnect the drive. No matter what gearbox you have, or how you change, there is always a short delay before the drive is restored. The car decelerates(sp?) during that time and if you change at the cross over point the RPM will drop below the optimum for the next gear.
Now, if you "over rev" it and change after the cross over point the RPM is right for the next gear to provide the maximum acceleration.
IF the gear changes were instant and the drive wouldn't be disconnected, then the cross over point would give the max acceleration.
The amount of over revving depends on the time the drive is disconnected and the deceleration of the vehicle.