Out of interest, what was the B race like post-sprint each lap - wondering if it was like ours?
Basically once you hit the top of Constitution Hill, all the way to maybe Parliament Square, the pace massively dropped off almost like the leaders were happy for the group to reform and everyone get their breath back. The race really only restarted again on the climb up Whitehall each time.
The tricky bit was that if you had sprinted and needed to recover or (like me) had not sprinted and rolled across the line with the intention of catching up to the leaders after the sprint, there was a big risk that you might not get back into the group in time. I certainly had to chase back on hard 3 or 4 times and very nearly missed the catch once or twice, but once I was in the group I was able to recover at 2.3-2.4 w/kg easily.