With that said, the recommendations (references not shown) if you load a car you need to add pressure. This pressure helps maintain the contact patch to the road. The load would "flatten" out the tires and increase the contact patch possibly causing overheating (the same problem with underinflation). Still you should not exceed the limit of the tire (read the sidewall). Extended highspeed driving requires a higher pressure of a couple of pounds to reduce heat. And your pressure will change 1-2 pounds for every increase or decrease of temperature.

As for auto crossing and Nascar, etc they constantly play with suspensions and pressure settings to max out speed. They also change tires often or don't worry much about long life. Drag racers decrease pressure for traction but they don't have to worry about going around curves. They also bolt the tires to the wheels so they don't slip off while spinning. There are a lot of things going on in the race world that don't apply to everyday driving