Some news on Intelligent Speed Assist.
It would seem Tesla has updated the user manual (at least for M3)
Excludes United Kingdom, Northern Ireland, Iceland, Turkey, Israel: A chime sounds when you exceed the determined speed limit and the speed limit sign flashes.
Note
For every occurrence, the speeding chime goes away after few seconds, or when Model 3 slows down below the specified limit using the brake pedal.
They are handling UK opt-out by not having the Chime on by default, only the visual alert.
Bad luck for the Rest of the continent though. It seems they'll have to put up with the chime or think to disable it "AT THE START OF EVERY DRIVE"....