pstaney,
The ECON mode of the FMS uses the inputted CI value together with the wind values to calculate the cruise speed. That really is the advantage of using Cost Index over a selected cruise speed such as LRC/MRC.
B777Heavy,
The lower CI value is very close to Maximum Range Cruise, so we would expect to have more fuel, however the trade off is between fuel cost and aircraft costs, so just because you saved fuel,it doesnt mean that you made money !
Mutt