Actually, in racing situations, a lot of the time cars wont down change unless they are sequencial gearboxes.
The car's are set up to brake with the braking balance, and adding the engine into that upsets the balance.
A V8 supercar will brake to the required speed, pick the appropriate gear for that speed then accelerate. This was tought to me by professional race driver.
Rally and F1 will downchange through the gears but only because they have to.