Six hours feels like you can function, until you can't. I think i remember seeing that people who could reliably function with just six hours exist but are vanishingly rare.
It depends on the person. Need for sleep follows a normal distribution in terms of what you require.
Natural short sleepers who only need 4.5 hours exist. Most people who sleep that much are chronically sleep deprived but there are people who just genuinely don't need that much sleep.
