You've pointed out that employees always produce more value for their employer than they receive in wages for that labor; that's how capitalism works. But has there ever been a systematic attempt to gauge exactly how much these numbers differ? I'm sure the rate must vary a great deal from industry to industry, business to business, job to job, but I'd be very interested to know if there are any examples of studies where researchers have attempted to put a numerical value on average exploitation of labor.
The short answer is yes, there have been many such empirical studies wherever Marxist economists have decided to "apply" the theory of surplus value to a set of concrete conditions. Such work continues to be produced.