777 Cost Index
If you evaluate fixed mach numbers ranging from .87 down to .76, you will see that the optimal mach in terms of arrival fuel quantity will always be .825-.83.
If you evaluate cost index values from 250 down to 0, you will find the optimal cost index in terms of arrival fuel quantity will always be 25-35.
My airline based in the USA uses these optimal values on ALL of our 777 operations. Everything from 800 mile domestic routes, to 6000 mile polar
routes.
Hope this helps.