My N=1:
I’ve done the same Turkey Trot for 5 years, exact same course. I have helped mark the course. We start at the exact same places. I am sure. And my garmin has read 6.15 +/- .01 all 4 years. For the last 4 years I have started my marathon prep coming in early October, and run 30-35 miles through out the summer. More or less everything has been the same. I am just older, turning 43 in 6 months.
My training has been consistent with other years. Nothing stood out, no training breakthroughs that I can imagine.
I guess what I am saying: as best I can tell everything was the same except the shoes.
38:35 in 2015
39:03 in 2016 (HOT out)
38:30 in 2017
38:08 this year
And it felt better. There is a U-turn in mile 4, so throwing that out all my mile splits were between 6:10-6:15 and I picked it up at the end and ran 5:40 pace for the last quarter mile. I run one 10k a year, and I am a triathlete/swimmer not a runner so I didn’t exactly expect to nail the pacing.
What this reminded me of was the first time I wore a full body LZR speed suit in 2009 (the one Phelps wore in the '08 Olympics). I had a mediocre start but went my fast 50 freestyle in 9 years.
These shoes - maybe - should be illegal. But since Nike has the “it” shoe no noise will be made about it. When someone comes out with a shoe that is better and cheaper the legality of the shoes will start to be questioned (When Speedo wasn’t making the fastest suit they were soon outlawed).