Rune Larsson is a ten time finisher of Spartathlon with the 23rd fastest time ever in 24:41. I read an article he wrote with his advice on how to approach the race. It seemed very informative and my favourite quote was:
"Set a clear goal. The goal should be related to Sparta. I used to have the Sparta Hospital as my goal. If I ran hard enough, I would be taken by ambulance to the hospital, where the doctor and nurses would give me the best care a collapsed runner could ask for. When I got exhausted towards the end of the race, I enjoyed the sensation, because it was a clear sign that I was on my way to being worthy an ambulance ride after touching the statue of King Leonidas."
That's giving it all you've got!!