From the International Game Developers Association, via the ever-helpful 43 Folders:
Why Crunch Mode Doesn’t Work: 6 Lessons

When used long-term, Crunch Mode slows development and creates more bugs when compared with 40-hour weeks.
More than a century of studies show that long-term useful worker output is maximized near a five-day, 40-hour workweek. Productivity drops immediately upon starting overtime and continues to drop until, at approximately eight 60-hour weeks, the total work done is the same as what would have been done in eight 40-hour weeks.
In the short term, working over 21 hours continuously is equivalent to being legally drunk. Longer periods of continuous work drastically reduce cognitive function and increase the chance of catastrophic error. In both the short- and long-term, reducing sleep hours as little as one hour nightly can result in a severe decrease in cognitive ability, sometimes without workers perceiving the decrease.

It’s hard to imagine “getting it all done” in 40 hours, but then again, it’s hard to imagine “getting it all done” in 60 or 80 hours either. As David Allen reminds us in Getting Things Done, if you have a creative bone in your body, you’ll never get it all done.
So I’m inclined to take the challenge and see what happens. You?