A specific Mach number is what airliner airframes are designed to fly at; it's absolutely the correct unit to talk about in this context. If airplane A is designed to cruise at 0.94 mach, it is faster than airplane B that cruises at 0.89 mach.
I don't understand the need for all the smoke and din in this argument thread. Old passenger jets flew a little faster than modern ones and that's okay!
