Perception comes into it I'd say, just as being comfortable at speed, as shown in some of the answers here concerning what different individuals feel as a comfort level at a given speed.
That's right, but you can have norms, the industry designs around some concept of what the public wants, even if they have different ideas about that. I also think different riders, as you say, will experience things differently possibly because of different weight, or objective factors as well as subjective factors. I think there are objective as well as subjective issues, or one couldn't design anything.