The maximum speed at cruise altitudes is actually a mach number. Beyond that speed, high speed buffet and eventually high speed stall will occur, as the shock-wave builds up.

Mach number is merely a function of true airspeed and temperature. In still air, that may provide a groundspeed of 1020kph, but at cruise altitudes, its very common to encounter headwinds or tailwinds of over 200kph.

In this instance, if you have a 200kph tailwind, you'll have a groundspeed of 1220kph.

At lower altitudes, the max speed is indicated/calibrated airspeed. That is, in essence, the force that the air exerts on the airframe. Going beyond that, as you have alluded to, will eventually cause damage to the airframe.

However, all our max speeds include a bit of a buffer, as safety margin. The test pilots have figured out the actual limits, and the manufacturer and regulating authority add a safety buffer to this.

Hope this helps.