> when you read studies, giving people 400 mg of caffeine (~4 cups of coffee) delays sleep by 30 minutes or so.

I'll need to see those studies. I'm finding the reverse: https://pmc.ncbi.nlm.nih.gov/articles/PMC3805807/

> One study examining the sleep effects of 400 mg caffeine administered 30 minutes before bedtime demonstrated both severe sleep disruption as well as important cardiovascular effects during sleep likely related to increased sympathetic activity.