Great co-workers, somewhat interesting work, insight into a really interesting organization, and a situation where I went in with too little information and now would face substantial costs if I back out rather than persisting for another 3 or 4 years.

That's fair enough, but I think your personal circumstances are unusual (and unhealthy). For the majority of people sleeping 8 hours is practical advice because they work 8 not 12 hours, leaving them with 4 extra hours, which is enough time to go to the gym, spend with family etc..