Is 6 hours of sleep good?

Neuroscience*: Anything less than 7 hours sleep is worse for your body than smoking. And where smoking affects certain parts of your body, lack of sleep affects virtually every system in your body.

8 hours recommended.

* Eg, Why We Sleep, Matthew Walker. Amazing read. Life-changing.

Depends on the person. Some people can function like a normal person with 6 hours sleep. Me: I shuffle around all day like an extra on The Walking Dead.

6 hours is survivable, 8 hours is recommended

Good enough. If it is sound.