This is back-to-back days, The "heavier" one on the left, the other one on the right. Course was about 98.5% the same, I took some opportunistic rights when available on the lighter bike, so it ended up being
that third of a mile longer. Some of the speed comes from weight, some from a more aero position, some from more gearing above 30mph, and I'm sure some from luck at lights.

Again, I would have imagined the variance to be much larger. Even with a slightly higher intensity (normalized power within 2%) it's something like 12 seconds per mile.
I mean, I guess that is a lot when viewed over time (over 20 minutes in an imperial century) but I think on some level we all imagine a change in orders of magnitude. But alas,
it's just a little bit faster at the same effort, and a fair bit faster with a little more juice put to it. I sweat a lot more the second day, when it was cooler. Go figure.