I always appreciate Ken Nakamura's stats, and reading just now his lists (posted right now on home page, and after that, probably archived or linked somewhere that I can't think of right now) of all-time marathoners by average of top 5 times, prompted a couple of thoughts and questions.
The top list for men is of course all Ethiopian and Kenyan, with a Moroccan or two (depending on how one counts Khannouchi in this list, as his times are part as MAR citizen, part USA). Who are the fastest top-five averages by non-Africans? If one takes Khannouchi's top-5 as a USA citizen, he is still under 2:07. As for non-African-born, I think it is Ryan Hall, whose top 5 average (assuming my quick math is OK), is 2:07:35 (rounding up to nearest whole second). Toshinari Takaoka's is 2:07:51 (I think).
Who was the first to have a top-5 average under 2:10? (Not a quiz -- I don't know, & haven't tried to look it up & calculate it.)
On the women's side, this top 5 average really illustrates Radcliffe's dominance (by this measure): her top 5 average is more than 2 minutes faster than Ndereba's (2:18:04 to 2:20:11). To contrast, Gebrselassie's top 5 avg is just 6 seconds ahead of G. Mutai's (2:04:57 to 2:05:03). Sometimes I forget how dominating Radclife's fastest performances are, but this shows it again.