Why do people get wound up about unreliable airspeed in the cruise?
When you get to cruise make a note of the pitch attitude and N1 setting?
If you get Unreliable airspeed, you have the couple that was working fine to start with.
Or turn to 2.21 of the QRH, go to the bottom of the page and cross reference......
CLEAN - FL - SPEED - WEIGHT - PITCH/THRUST at your current weight.
Read across the pitch/thrust tables until yours match! Its all in front of you and always has been.
(While you're at it, note the LRC and green dot driftdown flight levels in case.)