I think it will now default to 5 mph over if you set it? I forget. But I have had it slow down when speed limits change.
BUT you can always override while driving, and set cruise higher; I know I do.
BUT Autosteer will not work over 85 MPH. I have not tried to hit that; I generally won't switch on Autopilot at anything higher than 70, at this point.
It used to only get speed limits from GPS+Open Street Maps, but as of four days ago, it also recognizes speed limit signs.
I wouldn't try it in construction zones, they tell you not to. Here's an interesting story about someone who did:
https://www.reddit.com/r/teslamotors...on_worker_and/