Speed isn't as important as it used to be. Sensors, long range missiles and stealthiness have become more important than raw speed. Aircraft first broke the sound barrier (Mach 1) in the mid 1947. By 1949, warplanes could travel at Mach 1 relatively safely. At sea level, Mach 1 is 1,225 kilometers an hour, while at 20,000 feet it's 1,062 kilometers an hour, the difference being caused by varying air temperatures. It was eventually discovered that speed greater than Mach 1 made maneuvering difficult, and that most air combat was flown at less than the speed of sound. The human body literally could not stand the stresses of maneuvers at higher speeds. But for several decades after aircraft first broke the "sound barrier" (Mach 1), speed became an obsession. By the 1980s, no one bothered any more.
The top ten speed records are;
The American X-15 flew at Mach 6.72, at 354,200 feet in 1961. This has never been topped, and no one has really tried, as the X-15 was built just to test aircraft flying very fast and very high.
The next record holder is the U.S. SR-71 Blackbird, which flew at Mach 3.35 at 80,000 feet. This aircraft was designed in the 1960s to fly recon missions high and fast.
The Russian MiG-25 Foxbat-B flew at Mach 3.2 at 80,052 feet and was now used as a recon aircraft (sort of SR-71 Lite as it did not have the American aircrafts range).
The U.S. X-2 flew at Mach 3.2 at 125,907 feet, in a preliminary to the X-15 program.
The American XB-70 Valkyrie bomber flew at Mach 3.1 at 95,000 feet in tests.
The MiG-31 Foxhound, a development of the MiG-25, flew at Mach 2.83 at 67,600 feet.
The original MiG-25 Foxbat flew at Mach 2.8 at 67,915 feet and was designed as an interceptor (against the never deployed U.S. B-70.)
The American F-15 Eagle flew at Mach 2.5 at 60,000 feet.
The American F-14A Tomcat flew at Mach 2.4 at over 50,000 feet.
The U.S. F-111 Aardvark flew at Mach 2.4 at over 45,000 feet.
The Russian Tu-144 Charger (a failed competitor of the Concorde) flew at Mach 2.4 at 9,055 feet.
The Russian MiG-23 Flogger flew at Mach 2.35 at 59,055 feet.
The Russian Su-27 Flanker flew Mach 2.35 at 55,755 feet.
The U.S. F-106 Delta Dart flew at Mach 2.31 at 53,000 feet.
The fastest manned flight was not an aircraft, but a spacecraft returning to earth. Speed for these vehicles is as high as Mach 37.