It's mostly just practice & experience.
But TBH, 50+ starts feeling sketchy and then you start thinking things like, "What would happen if I took a spill at this speed...?"
When I get that thought, I slow down. I don't push it when I have bad joojoo.
You're right though, top speed you really start focusing hardcore on what you're doing. I tried to explain it once as having terminator vision, imagining the terrain gridline, little squares identifying potential hazards and as speed tracker in the corner showing your speed. haha