To be as productive as you can, never cheat on sleep.
Proper exercise and diet is good but those not to be used as substitute for sleep. Recent research has show sleep improves ones cognitive skills, intelligence, concentration, body weight, improve the health of the heart. There is no substitute for sleep
If you have to wake-up by using the alarm clock or some one else then you are not sleeping enough. If you have to wake-up like that, then find some time to sleep later in the day or weekend to make for this deficit.
I am sorry to disagree with most of you, because I don't believe there is a healthy substitute for sleep. If you think you are fine now with less sleep you are not operating at your best. You could do better with more sleep. It may take up to 4 weeks of sufficient sleep to realize this.