You're asking different questions and mixing different reasons. Is it a problem of what's better for your health or what's more practical for work? The article

You're asking different questions and mixing different reasons. Is it a problem of what's better for your health or what's more practical for work? The article anyway talks about 6.5 hours average and defines deprivation as less than six. If 6.5 is enough for you, good. As for you need to wake up at certain time... you still can go to sleep earlier. Yes, I know. That's difficult and you miss other things instead of work, but you should know what you're trading sleep for.