How do the training techniques vary when you start dealing with races of 70 miles, 100miles, and 250 miles... ?

In a once day spurt Those are the things I want to do. Completion itself is a huge bonus. But, how does one attempt it competatively? i'm looking at the results from one local 252 mile race, and no one is even accomplishing platinum, and they are spread out far, so pacelining isn't as big a thing (not enough starters?) when you start dealing with over 200 perhaps? Or maybe that race isn't as big a deal. I know that at El Tour, they're still pacelining heavily, and accomplishing some amazing speeds considering the distance.