top speed of boeing 747 airplane

the cruising speed of Boeing 747 is around 0.85 Mach,A 747-400 typically takes off at 180 mph (290 km/h),
The 747-400ER range is approximately 7,720 statute miles (14,297 km).
Engine thrust has as much as 63,300 pounds (28,710 kg).
The 747-400 tail height is 63 feet 8 inches (19.4 m), equivalent to a six-story building.
They could probably go a little faster than this as limiting speeds on airliners are usually created with some safety margin - assuming they could push mach .95 in a dive The Boeing 747-400 can exceed 600 mph if you aren't careful.
The top operating speed (never exceed speed) for a 757 would be .86 which equates to about 550 MPH groundspeed at somewhere around -20 degrees Fahrenheit (my guess for the temperature between 30,000 and 40,000 feet) - if the pilots kept the speed up in the descent and maintained a mach number of .86 this would rise to around 630 mph groundspeed as they neared the ground on a warm day.