Hey Barton Fiske, the answer changes every month actually. I love to experiment and see what works best for me, because as you said, the best is not the same for all. I used to be insanely tired when sleeping 8 hours. I only realized years later that it was because I would always wake up in deep sleep.
Given our 90 circadian cycles, I decided to give other sleep amounts a shot. I now try to follow a number of full cycles. For example, if I sleep 7.5 hours, that’s 5 cycles. It’s much worse for me to wake up after 5.x cycles than it is at 5. Ultimately, I aim for 4 or 5 cycles. My norm is closer to 4, but after a while it gets tiring, so I go back to 5.
Hope that clarifies it!