There's no priority combination where sustained 60-80 hour weeks make sense.

Looking to prove yourself? You can't sustain that long term, at least not at the same quality, so you're just setting unrealistic expectations and setting yourself up to disappoint your boss.

Your boss told you to? If this is meant to last longer than 2 weeks, he's setting all his subordinates up for burnout, and quality will suffer. Don't let your boss set everyone up for failure.

Personally, I've found that 60-80 hour weeks is okay for a 2-week crunch. Then you need to recharge for 2 months before you can do it again. So treat crunch time like any other limited resource, and use it sparingly. Boss just wants it fast? Tough shit, it'll be done when it's done. Half the company is blocked until you fix this thing? Crunch time.