I tracked myself with apps for a couple years, various apps and various phones. My top speeds (after correction) were consistently anywhere from 100-130 kph each day.
I bought a Garmin GPS watch this year (after losing a phone on the hill) and was expecting similar results. My boarding hasn't changed, in fact I'm likely going FASTER as I'm used to the mountains more this year, but the top speeds have gone down to the 70 kph range at Fernie and Lake Louise (more off piste), and the mid-80 kph range at Nakiska (groomer bombing/hard carving).
The other thing is, my max speeds used to fluctuate by 20 kph a day at the same hills. Now it's very consistent. All my max speeds since changing to the watch (about 30 on hill days ago) have been within approx 15 kph over ALL the hills.
Next time I'm out, I'll take a smartphone with the app and run the GPS watch at the same time.
Overall distance will be reasonably close, although the apps don't pick up carving. Max speed for the day is just so random that looking at an app and saying things like "my max speed is higher than yours because _____" just doesn't make sense.
The apps are fun, it's a great way to push yourself for longer distance and vert each day, just ignore the max speed readout. It shouldn't even be there...