This is fascinating. Not just about bragging rights, but real research on crazy high speed in the atmosphere, and reentry from space.
The X-15's highest speed, 4,520 miles per hour (7,274 km/h; 2,021 m/s),[1] was achieved on 3 October 1967, when William J. Knight flew at Mach 6.7 at an altitude of 102,100 feet (31,120 m), or 19.34 miles. That X-15 never flew again as the skin was just torched with holes burned in the skin.
Almost as fast as our Cessna 182! 