What am I missing?
Actually, it makes most sense to first aim for the 1,235 km/h mark, the speed of sound. The added benefit is that you break the current record of 1,228 km/h which narrowly avoided breaking the speed of sound by only 7 km/h.
On October 15, 1997, in a vehicle designed and built by a team led by Richard Noble, Royal Air Force pilot Andy Green became the first person to break the sound barrier in a land vehicle in compliance with Fédération Internationale de l'Automobile rules. The vehicle, called the ThrustSSC ("Super Sonic Car"), captured the record 50 years and one day after Yeager's first supersonic flight.