That's interesting, thanks...never heard of planning a flight using cost index...
Sounds like cost index is tied to fuel burn.......
As a general rule, when the fuel prices were low, going fast made sense, as engine overhaul costs outweighed the fuel burn savings...when fuel prices were stupid, some peeps were pulling the levers back...
I found that as a general rule, if I could eliminate some of the stops and fuel purchase, and cycles, that really saved some dough...