Straight from the Boeing technical/test team..... The unreliable airspeed Pitch and Power settings are for one purpose and one purpose only. To stop you damaging the aeroplane.
An incredible amount of time and effort went into developing the memory item numbers as they must cover all weights and altitude scenarios. If you are high and heavy you will descend if you are light and low you will climb but you will never stall and never overspeed with these numbers. It is also assumed likely you will have begun to lose control of the aeroplane before an unreliable airspeed diagnosis hence the importance of the numbers. Airmanship always supercedes any Boeing QRH. There is no requirement to set these numbers if you are entirely satisfied with current and correct pitch and power after the failure and situational awareness is firmly intact.