So I ran Broad Street last weekend (like a chump). My chip time was 1:57:31 (because I'm slow and 10 miles is a long damned way...also there was a ~5 min bathroom break in there). For those who are passably good at math that translates to an average pace of 11:45. Not great, though better than last year despite not properly training and having sprained my ankle pretty badly ~3 months before. Also I know the last mile was right around 9 min from the clocks at miles 9 and the finish. Then I checked Map My Run:
10.58 miles in 1:54:13, or 10:47 pace
Now I may have missed turning it off for as many as 200 m past the finish line, and clearly my bathroom break was auto-paused away--not 5 min, but it was probably another 1-2 min before I actually stopped it after the finish. But most of that added distance is because we didn't run a straight line down the street, cutting all the corners as short as possible, and over a 10 mile stretch little wiggles here and there (water breaks, finding shade, swinging wide to get more space) add up to nearly half a mile over the nominal race distance. Now I don't know what the error is on those numbers but based on comparisons to my bike computer (which I trust to better than 95% confidence), it's pretty good.
10:47 is quite a bit better pace than 11:45.