The official marathon world record is 2:02:57, run by Dennis Kimetto in Berlin in 2014. Berlin is the best course in the world for a men's marathon world record attempt; the last six men's world records have all been set there, dating back to Paul Tergat's 2:04:55 in 2003.
Six of the ten fastest men's marathons ever run were in Berlin, and six out of eight if you take out the wind-aided runs from the 2011 Boston Marathon.
Kipchoge's 2:03:03 personal best is only six seconds shy of the current world record. 2:02:57 is 4:41.5 mile pace for 26.2 miles.