Curious, do you manage to fall asleep by 8 or 9? I'd love to get up early more regularly, but I find it tough up turn my mind off before the world quiets down.
I've known a few people who were fine on 4 hours a night. just the way they were built. for me, less than 7 and I simply can't concentrate on anything all day, til about an hour before my next bedtime...
Scientific evidence matches your anecdotes. There is a very small percentage of people whose genes allow them to only need 4-5 hours of sleep each night. It's somewhere in the low single digit percentages.
For the rest of us, 7-9 hours are required for proper functioning. If we get by on less, we're functioning suboptimally whether we realize it or not.
Mostly on work days (weekdays), throughout the day I have plenty of energy but around 9:30 I start yawning and the exhaustion kicks in. I don't drink coffee or anything to get through the day.