Hot Face
...
Long drive contestants always have a bag full of drivers - names like Alpha, SMT, Bang and Ashton - built to withstand competitive abuse of swing speeds north of 140 mph. They constantly test their drivers to try to figure out which one will perform best. One of the tests they use is to lay the edge of a credit card across the face of their driver. In time, the driver face begins to flatten. At that point, the face has weakened. That's also the point when it flexes the most, when the face is the 'hottest'. Once the heads reached this stage, they are reserved for competition.
...
The flex and hot face mentioned above also known as the trampoline effect... Where USGA has limited it to 0.83 COR..So I guess keep using the same driver.... If change to a new driver, buy it used and always carry a credit card for measurement.... After all, it is true that the more and hard you drive, the further the ball goes...

*source: GolfTodayMagazine.com