While I'd be useless for everything when I sleep 5h, my sweet spot is between 6 - 7.5h. I used to try and get 8h+ of sleep and was often tired.

Now I set my alarm for 6h after I go to sleep (leaving 15m to fall asleep), have snooze set to 30m and max 3 times. Additionally I need to solve a simple math equation so I don't mindlessly press snooze. That way my amount of sleep varies on what my body feels it needs. Feeling way better since the change :)

Just an anecdote so take it however you want :)