quote from link "Ultrarunners are an idiosyncratic bunch. They practice the sport in a thousand peculiar and individual ways. But on any given weekend, a high percentage of them will all be doing pretty much the same thing: completing a long training run. Thatís because the long run is widely recognized as the most important element in the ultrarunnerís training regime, especially for the beginner."
I guess this article proves that crossfit endurance will not work if you want to make it to the top in ultra endurance events. CFE might get you fit enough to finish 100 miles but to finish at the top it looks like one long run a week is needed