The thing is with a cost index of say Zero, there's practically no increase in fuel gain but a time lost of almost 6-7% ie. 4-5mins every 1 hour. for a 10-hour flight, you will be talking bout 40-50 mins of later arrival!
unfortunately, boeing's text clearly states Zero cost index gives you MRC. clearly this doesn't seem to be the case in real life? does this happen to others or is it just me?
SR