From Airbus ''Getting to grips with Aircraft Performance'' 2.2.4:
'To minimize overall fuel consumption during flight, a low CI must be used. As the climb phase is fuel consuming, it is advantageous to minmize climb duration. This is achieved at the maximum rate climb speed. CI 0 gives IASecon which is Max Rate Climb Speed.'
It seems to work out most times about 270KIAS in the A319.
For the above publication, Google 'Wing Files'
Cheers all,
mcdhu