The page http://www.turing.org.uk/scrapbook/run.html give's Turing's marathon time (August 1947) as 2hr 46min 03sec and the winner J.T.Holden's time as 2hr 33min 20sec. Contrasting this with wikipedia re the 1948 London Olympic marathon http://en.wikipedia.org/wiki/Athletics_at_the_1948_Summer_Olympics_–_Men's_marathon we see that Turing's time would have been good enough for him to place 15th out of the 30 finishers (41 starters), whereas Holden's time would have been good enough to just win gold. The Olympic course and/or conditions presumably were tougher, but even assuming that is worth 5 minutes, which is probably an overestimate, then Turing still would have placed 20th in the Olympics. Not too shabby! Turing was probably the world's fastest mathematician, (before say, 1970, anyhow).