Uhhh, does that actually say what you want it to say?

The summary of the chart in the second link is roughly:

  hours   productivity   product
  40      100%           40.0
  50      90%            45.0
  60      83%            49.8
  70      69%            48.3

So productivity per worker rises until around 60 hours per week, but productivity per worker hour is decreasing the entire way through.

What this means is that 60 hour weeks only make sense if your labor cost per worker is fixed, not your labor cost per worker hour. It doesn't make sense even without overtime pay, but if you're paying someone time and a half to work 60 hours a week, you're paying for 80 hours and getting 50 in return. You'd be much better off paying two workers for 40 hours a week each and actually getting 80 hours of work for those 80 hours you're paying for.

As an individual, working 60 hours per week regularly makes sense if you're a self-employed author and can't hire someone else to get the extra 10 hours of productivity, but if you're the average salaried slob working for the average company, it's a terrible bargain. You make the same pay, and the company gets 10 hours of extra work while you lose 20 hours of extra time. Why the hell would you agree to that?