Sheldon states-
"•An overinflated tyre will have slightly less rolling resistance if the surface is very smooth..."
FME, at the specified manufacturers limits of the tyre, the possible gain or loss might be be miniscule.
Small enough, that it would only be in your head.
Foo is spot on, and something to be aware of, the specified pressure stationary, will change during
a competiton, and chances are, in longer events, increase. Atmospheric conditions count.
An overinflated tyre will give you a very rough ride, with the possibilty in bends, of bouncing
and losing traction, and a fall, so there are the other competitors to consider. If not yourself.
Also an overinflated tyre in competiton, especially in longer events, are more prone to puncture,
which, if your there to compete, could put you out of the race, in an instant (and a fall may occur)
So all things must be considered. What is the "perceived" gain? (if any)- against, the consequences.
Better safe, than sorry.
Better to be there at the end of the event, to do your best, that's where the winners are.
Begin with manufacturers' specs. Those are my thoughts.
Cheers

Lone Rider- I rode on the long, dark road... before I danced under the lights.