For the duration of his life I've operated on 5-7 hours total every night. I (and my co.) were just acqui-hired, but prior to that I was in the 5th year of startup hustle, which became infinitely harder with a newborn.
The difference is that I appreciate the value of sleep more than I did before. During a near-acquisition a few years ago I was sleeping 3 hours a night thinking this was the solution to deadlines.
For anyone who has lived through that first 6 months or so, you know you never really sleep. Even if you get 6 hours, it's peppered with wakeups, rockings, diaper changes and feedings.
Last night I slept about 5 hours and I feel the way I used to feel with 8. This could be a function of age, but I feel like my body is acclimating to an abbreviated sleep schedule. This has led me to believe that people who "need" 8 hours of sleep can train their body to need less.
That said, if you can sleep, for god's sake do it. Once this kid starts sleeping past 6:15 I'm going to go nuts on the weekends.