Two problems with this are 1. It is very difficult for outside employers to tell is someone is a high performer, and 2. Economists also teach to always think on the margins. A employees value isnt the amount you bring in more than if they didnt exist, it's the amount they bring in over a replacement. If people are willing to replace you for $5/hr even if you make the company $100/hr you wont get anywhere near that amount.