That's absolutely true with me. I am at peak performance after about 5 hours of sleep. After that much sleep, I am always ultra alert and focused throughout the entire day.
When I was infantry school, we'd only sleep 7 hours a week and it was hell but you get used to it to an extent. Then you walk around like a zombie, you are a awake but you are in constant state of meditation. You can't think but you can focus on the task no problem.