For the 744, max speed is .92, or .90 in RVSM airspace.
Normal descent speed is roughly the same as cruise mach, or .83 - .86, until intercepting about 290 - 340 KIAS at lower altitude. These will depend on gross weight, selected FMS Cost Index, and airline FOM.
Typical would be .85 Mach to 310 KIAS.
Minimum varies with gross weight, but would seldom be below .80 except in unusual circumstances (e.g., ATC restriction).