Im the same way, cept Ive never gotten just 4 hours of sleep before. But I know if I get 6 hours of sleep, Im dead, and if I oversleep Im dead, though most of my oversleeping is between 10 and 15 hours of sleep, so most of it doesnt fit in the 4 hour increment thingie.
I think Ill try 4 hours of sleep tonight, see how I do in the morning. Cant be any worse then the 7 I usually get.