I am horrible at going out too hard. I just feel good at the beginning and forget that I will feel like hell later by keeping the fast pace. I remember the worst example was my going for a 7 minute first mile at the beginning of a 50k... It was also my first marathon or longer run... I made it but holy crap that first mile destroyed me for later on.
I find audiobooks to be the best for me as music makes me want to run to the beat where the books allow me to find my own tempo.
I've not done a 50k before. Best I have done was a half marathon. kudos to you for accomplishing that.