Rudisha's WR and Olympic gold was the best performance of the year, but we are talking "significant" here.
To me, significant means that it could change the way people think, or change a group of atheletes' take on an event. A significant performance (like Bannister's breaking of the 4 minute mile) changes the way people think.
Male distance running in the past 20 years has been dominated by African born runners. Arguments were made that Europeans and Americans didn't genetically stack up or couldn't put the work in to win a distance medal.
The genetic argument was not offered too often as it was seen to racist, but inside distance running, it was often referred to. For years American and European distance runners seemed to give up, and the media tried to find new endurance events (Triathlon) to cover and televise over distance running races. The European and American interest in distance running wained.
Along came Galen Rupp from Oregon, born and trained in the US, winning the silver medal. Caucasian runners, born and trained in their home countries now know, if they work hard enough, for long enough, they have hope to race with and challenge the great African runners. This is very significant - the most significant.