I excelled when I was a MS CS student at Stanford (I can go into detail if anyone needs convincing), and I did it on very little sleep - 4-5 hours/night for weeks at a time. I absolutely positively couldn't have done what I did on 8 hours of sleep a night. There wouldn't have been enough time in the day.

I sleep much more now. Left to my own devices, I adjust to a roughly 28-hour clock during which I sleep 9-10 hours a cycle.