10X 800 with equal time recovery is supposed to be predictor of your marathon time. Bart Yasso made a huge name for himself and probably a couple or few million dollars out of popularizing the concept. Yasso's have been largely discounted as a spurious artifact, in that they are not actually a predictor of marathon potential because if you are reasonably fast twitch or in good enough shape you can run what looks to be a good time, while still not being able to cover the marathon.
That said, for college XC that was basically our go to October Wednesday workout. We were overtrained and flamed out at the conference meet every year.
