I didn't see Sorensen's power file yet, but I saw the screenshot of Horner's. 5.9 w/kg for 30 minutes in the front group, a minute down. Doing the math in my head, and without seeing the stage, I'd guess there's a 6.5 w/kg 5 minute section in there, with an overall of roughly 6.2 w/kg. For 30 minutes, that's certainly a lot, but doable, particularly on the first climb of the day.
It's a far cry from 6.7-6.9 for almost 50 minutes, that's for sure.