I made it to Chicago and was talking to Sean Hartnett, marathon cartographer extraordinaire (he makes a lot of the race topographic maps and helps the races with pacing). Sean was in Berlin for the world record attempt and helped Berlin create a system that gave the leaders a split every kilometer, and showed their projected finish time on a clock on a vehicle in front of them. He'll have a similar system in place for Chicago this weekend.
I asked Sean what the fastest finishing time his projected clock showed and he said at 37k it showed 2:02:40.
The slowest it showed I believe was in the 2:04s around 10-12k.
Sean and I were talking about how much faster these guys are running than even Paul Tergat a few years ago. Sean said some of them have said the clock and splits makes a big difference because it doesn't let them take the foot off the accelerator during the race. Every km they can see how they are doing.
Sean said Tergat's general view on the marathon to get the WR was to run 3:00 (2:06 pace) a km for the first 20 miles and then try and run sub 2:55 the last 10k.
Now they are averaging 2:55 for the full marathon.