I know it is best double, but here is a run down of the Nurmi 1924 Olympics. Keep in mind temperatures in Paris were in the 100s.
July 8th
-Wins his 5000m heat
July 9th
-Wins his 1500m heat
July 10th
-Wins 1500m in an OR
-Wins 5000m in an OR(30-45 minutes or so apart)
July 11th
-Wins 3000m Team race heat
July 12th
-Wins XC 10,000m Gold in +105 temps. He runs a 32:54, third place runs 35:21.
July 13th
-Wins 3000m team race
Also overshadowed by Nurmi, but Ville Ritola also had a insane 1924 Olympics. Won Gold at 10,000m in a WR and OR in Steeplechase.
Here is Ritola's Olympics:
July 6th
-10,000m Gold, WR by 12 seconds.
July 7th
-Wins Steeplechase heat under old OR
July 8th
-Finishes 3rd in 5000m heat
July 9th
-Wins Steeplechase Gold beating old OR by 10 seconds.
July 10th
-Finishes 2nd to Nurmi in 5000m final by .2
July 11th
-Finishes 2nd to Nurmi 3000m team Q heat
July 12th
-Finishes 2nd to Nurmi in XC
July 13th
-Finishes 2nd in Nurmi in team 3000m race.
Here is Zatopek's:
July 20th
-Wins 10,000m Gold in OR
July 22nd
-Finishes 3rd in 5000m heat
July 24th
-Wins 5000m Final in OR
July 27th
-Wins Marathon Gold
I guess you can argue Zatopek had better competition in a more modern age, but I still take the Nurmi double.