Most executive jets (business jets or private jets).
They all compete with each other, and each is now reaching 0.94 Mach.
Yes, 0.94 Mach!
Each has special exemption from FAA to fly at heights well above the 41,000 feet ceiling the FAA imposes for transport category aircraft. Many have service ceilings at or above 51,000 feet. That enables them to fly faster; good aerodynamics, upset-recovery training (UPRT), and smart systems ensure they do not get into the difficulties earlier jets used to get into at those altitudes.
▲Cessna Citation X+: The latest member of the Citation family, the 2010-launched Citation X+, is the undisputed king of speed, and can sprint at mach .935, or 717 mph, making the trip from Los Angeles to New York in under four hours.
▲Dassault Falcon 7X: One of only two “trijets” currently in production, the $52.5-million Falcon 7X was, when launched in 2005, the first ever fully fly-by-wire business jet. In 2014, a 7X made a record trip from New York to London in under 6 hours, an entire hour faster than the average commercial flight. Top speed: mach .90, or 690 mph.
These records are temporary: look to the manufacturer’s latest models for current data.
Transport category aircraft seem to have stabilized at between Mach 0.85 to Mach 0.88 best speeds. What cruise speeds they fly at is quite different, decided by the Flight Management Computer according to the criteria you have set (usually, fuel economy).