Sleep Time vs. Efficiency?

It depends on the type of work for one thing. If you worked in an embly line, I suppose you could work for 8 hours theoretically, and accomplish something measureable. But imagine if you had to do a number of tasks in an office. If it's a Dilbert style office, you probably would spend at most about 3 hours of real work, and the rest of the time doing pretend work like staring off into space, checking your email, getting up to get coffee. If it's a job like that, working all night would not help that much, as you'd just do it slower and worse the next day.