A little worried I had gone through a speed camera a little too quickly, so I:
Pulled the dashcam footage (it doesn't overlay speed).
Measured the distance along the white markings using Google Maps.
Cropped the video clip in iMovie to start/end as I crossed the start/end of the markings.
Calculated that I was probably going 27mph (under the limit).
My brain can rest easy for the remainder of the day.