I'm fairly close to this. I used to require almost exactly 4 hours of sleep a night, and getting more or less than that made me feel absolutely abysmal, but over the years it's jumped up to 5.5 hrs/night with it being slightly more forgiving about the range (from 4-6 hours I feel decently okay, best at 5.5 and worse as I fall away from that, but outside of that band I feel completely horrid). I get more rest than this, but the extra hours of rest are usually laying down listening to music or the occasional audio book.

I think the biggest agent of change is my autoimmune disease which has worsened over the years and now requires of me more rest and sleep maintenance.

Got a cruel reminder of all of this sleep-related business last night with the bay area thunderstorm waking me after only 3 hours of sleep and the storm and heat keeping me awake until my body screamed for a rare noon siesta.