In the early 1900s, Ford Motor ran dozens of tests to discover the optimum work hours for worker productivity. They discovered that the "sweet spot" is 40 hours a week — and that, while adding another 20 hours provides a minor increase in productivity, that increase only lasts for three to four weeks, and then turns negative.
Anyone who's spent time in a corporate environment knows that what was true of factory workers a hundred years ago is true of office workers today. People who put in a solid 40 hours a week get more done than those who regularly work 60 or more hours.
Adding to that, Inc. mentions that people who work long workweeks have a higher chance of burning out. What about you — do you work more than 40 hours a week?