For me, the marathon is the true test of my long distance skills. It is much closer to racing a 10k than any
ultra distance. I have raced 100ks on the road, which I felt was my best test for ultras and a challenging
under taking. For me, I don't need to test myself against extreme heat or cold, or mud for that matter. It
doesn't appeal to me though it looks like it may have been platible 20 years ago.