There are two limits: 60000ft and 1000 knots. Some manufacturers use "AND" between them, others use "OR"[1]. So you can have faster drones if you manage to stay below 60000 ft.
Which is weird, because something traveling at 1000kts at 100ft seems scarier than something doing 1000kts at 60000ft.
Something traveling 1000kts at 60000ft can reach a target at 100ft. The legal guidance has ICBMs in mind.
Only if you're military or part of the government in the US, because civilian drones have a 100mph speed limit and a line of sight requirement.
Some manufacturers have imposed lower limits eg some older Garmin handhelds won’t display info at speeds over 90 mph, though they still maintained a fix. I believe it was to stop people using them in light aircraft.
That's probably because Garmin also makes avionics and flight systems, so they just segmented the market.
I have a Garmin GPS watch for jogging, and it worked fine at 700kph during a flight. Really helped my monthly average running speed.
The US got rid of the altitude limit a few years ago, and increased the speed limit to 600 meters/sec (about a 12% increase)