Good Going timzsta
Have to commend timzsta's reply. Your grasp of the theory is impressive for someone who has not flown airline jets.
I think your explaination provided the best answer to the question asked on this thread. I have flown B737-200s for a while and your numbers were spot on. Our company used 0.74M for our cruise (this is also the speed limit for a mach trimmer failure so a good choice). We climbed at 300 IAS till cross over and then 0.74M. Normal descent was at 0.74M then 280IAS. We would use 300IAS only if we needed to expidite the descent or were high. Of course as you stated, we would slow down to meet ATC speeds.
I enjoyed the question posed - nice example to illustrate the complexities of jet flight.