Well, I would say that cross country racing in high school prepped me pretty well for the intensity part of 'cross. That's 17-18 minutes (for me as a back- mid pack varsity runner) of fairly high intensity. A cross race is longer, and probably averages a lower physical intensity, however that is because on technical sections, etc, you'r enot putting out maximum effort because you have to focus on bike control. This is what makes riding more fun than running.
I've never done any bike racing other than cyclocross and some short track MTB, so cyclocross actually feels pretty long to me. However if I came from Road or XC, or especially endurance MTB, that would be way different.