At the end of the day... what's to be gained by flying at .80 and 320 Kts on descent? Noise and discomfort the folks in the back of the jet. Do you really save that much time? No.
Now if you're talking about the 727... different story. The 727 can easily lope along at .875 without breaking a sweat... Time will be saved over .78 cruise with quite a fuel burn penalty. But flying cargo back in the day cost was not the motivation... on time performance was.
I'm no boy scout by any means... however, I'm always thinking about how much extra gas I can keep in the tanks if there's a bit of extra holding at my destination regardless of weather conditions.