Several sources.
I kept track of the average charge rate when I go to Superchargers. I have done many road trips I would estimate about half of my 32k miles are done with Superchargers. The average is around 70 kW from real world usage.
Here is some data in a chart that shows very similar numbers
P85D trip SF-Portland: detailed data on range and charging
Someone here in the forum did a side by side Supercharger test with an A pack and a newer pack. He put together a graph showing the charge speed. The difference was pretty small and after a certain time both are identical. And again, that was starting from a low state of charge and not sharing a Supercharger. In the real world it isn't that way all the time. If you do a search here in the forum, you'll find the thread.
Here is one graph:
Older Teslas limited to 90kW Supercharging - Page 129
still trying to find the other where it's actually a real side by side.
PS: For the past few months I have never been able to charge at more than 105 kW, no matter where or what state of charge. Not sure why, my car used to charge at 120 kW when it was low. So it looks like getting the full 120 is not a given all the time.