Just took the data from the marathon website and worked out the 5K splits (spurred by coach observing that I had not slowed down nearly as much as I might have!).
Race map is annoyingly in miles rather than kilometers, and I am too lazy to sort it out, but I can say subjectively that I walked a couple short steep hills in Manayunk (figured it was not worth letting the HR go up) and felt least good (not terrible, but not great) at the 20-mile turnaround point which comes at the end of Main Street Manayunk, I am not surprised that my slowest chunk was the 30-35K stretch - it was actually all good from there, I felt strong in the last six miles.
That sort of 10:15 mile pace I had in the 35K-40K stretch (I think I was running very steadily, I didn't walk at all during the race other than through slippery aid stations and a couple short late hills) is very comfortable for me to maintain for a long time...
Must get back to WORK, marathon musings are distracting me from my real responsibilities!!!