Being on the lardy side of svelte as I currently am ('work in progress' if ever there was!) I tend to ride at 55psi for everything.
I'm guessing you're riding a hardtail as BiTD I never 'rode' over roots, choosing to lift the front or bunny-hop any and every obstacle; single track at speed, clearing obstacles then hard on the anchors to change direction was where it was at for me. I've never 'dropped off' anything in my life, especially on an XC bike.
Grinding up silly steep hills on an Onza stainless granny ring used to be fun when I was half the age I am now but these days I'm a bit of a wuss, preferring the ease of flat trails to anything that exposes my lamentable fitness! :facepalm: