I remember when Eliud Kipchoge first broke the 2 hour marathon barrier (although in specifically controlled conditions with multiple pacers, not in a proper race like Sunday), a few weeks later they set up a treadmill at a running Expo, configured to the average pace he ran the full distance at and asked all-comers to try and see how long they could last on it. Most people barely made it 200-300 metres before falling off the back!
Don't know about the last 5km, but between kms 35 and 40, he was 2 seconds faster than the current Parkrun world record (13:44).