There's been some discussion in the Aouita/Webb thread about the world records of the past which led me to this question:
What do you think is the greatest performance of all-time adjusted for era?
We often talk about one runner being better than another because of the era in which she or he competed. My first marathon would've been good enough to win at the first Boston and the first Olympics as well, but those guys were better runners.
My pick is Bob Beamon's 8.90, which is still the second-best performance of all-time 40 years later. Coe's 1:41 is second and at the top if we're considering just running performances. This is just an impression, however. I welcome more thoughtful and better-researched responses.