Some may remember Ernest K. Gann's comments in "Fate is the Hunter" about when his airline started flying Transatlantic flights in DC3s at the beginning of the American involvement in WW2.
The performance experts came up with plans to fly at really low power settings and (in the minds of the line pilots) ridiculously low cruising speeds to extend the DC3's range.
After two or three crossings, one of the older captains set out using the standard, higher power settings for the climb and cruise - and not only got to his destination quite a lot earlier, but burned no more fuel than they'd been burning using the low power/ultra coarse pitch settings.
Somethings never change?
I must add that from my observation on the 773ER, slowing down does save fuel, although I was taught when I first came on to the aircraft that it was a ".84 wing". Certainly anything over .84 is quite costly, and for minimal savings in time.