This is a pretty informative list and puts perspective on speed at various distances. This list focuses on North American runners, but also shows the current world records.

What did I learn from this? I learned that stopping 7 hours early in a 48 hour race kept me from having my name on this list. Winning is great but having my name listed among these guys would have been pretty satisfying.

I'll do it right next time.

http://www.ultrarunning.com/featured/ultrarunning-magazine-all-time-lists/