But is your overall productivity higher with 55 hours than it would be with less hours? It's the kind of question where I wouldn't really believe your answer,

But is your overall productivity higher with 55 hours than it would be with less hours? It's the kind of question where I wouldn't really believe your answer, unless you've actually tried to experiment yourself where is the cutoff (for your specific situation) between hours / productivity. Not because I think you would answer in bad faith, but because it's a really complex question. What if working less hours over multiple years would let you pursue some hobby, turn you more sociable and thus a better leader/CEO? Or maybe it would make you just very slightly better at decision making. You would have less time to manage your company, maybe relying more on others, but in exchange you would have more energy for the really crucial decisions. Or enough energy for extending that 2-weeks international crowdfunding effort into a 3-weeks.