They have estimated he saved 4:35 from drafting compared to a solo effort without any pacers or a pace car.
Interestingly, they estimate that of this 4:35 that only 26 seconds came from the Tesla car that received a lot of attention and 4:09 came from pacers in their delta drafting formation. So the car on its own, contrary to initial belief, had very little effect, but overall drafting was HUGE.
The say, "We think that the "large clock" took more of Kipchoge's publicity than it deserved... However, despite all of the â€œmarginal gainâ€ type improvements that Nike publicized in the lead up to this event, the evidence suggests that the vast majority of the performance improvement achieved was down to aerodynamic drafting...if you could organize a group of pacemakers that were capable of running in formation for most of the distance (instead of illegally relaying as in the Nike project), then you could probably get the legitimate world record close to 2:01:00."
Their article is here:
Beves and Ferguson didn't estimate how much drafting effect runner's get in a normal marathon. Alex Hutchinson of Runner's World has a nice article summarizing Beves and Ferguson's piece. In that he says to estimate that "divide the result by somewhere between two and four". Not sure exactly how he got that number but that implies that the special drafting accounted from between 1:09 and 2:17 of Kipchoge's improvement in time compared to a normal marathon.
Hutchinson briefly touches on this in his piece but it's not discussed in Siemens piece and that is the car helped set the pace and made the pacemaking easier for the pacemakers. It shot out a green laser that showed the pacers the right formation to keep and kept close to the right pace for the pacers. Hutchinson notes in the test event without the laser, the pacer formation fell apart. We don't think it would be as easy for the pacers to keep their formation on their own without this at this pace, but who knows.
Hutchinson article: http://www.runnersworld.com/sweat-science/did-the-tesla-pace-car-aid-eliud-kipchoges-20025-marathon
In totality, this sort of summarizes what we all knew, Eliud Kipchoge is still the greatest marathon in the world. He didn't radically become a different marathoner in the last 6 months, and we're still a ways from a 2 hour marathon in traditional conditions. Better pacing formations could help us get there quicker.