TrainingPeaks is offering up stage data files on riders they work with.

Just go here: https://www.trainingpeaks.com/tour-de-france/

(you do need to share an email address for access)

For the Stage 3 TTT, Matt Hayman had a normalized power of 348w, which included a half-hour of cool-down.  Take that out, and it’s easy to see his average power up near 400w.