A320 Ci
In general the lower the CI the steeper the climb path, the shorter the climb distance and the nearer the ToD basically because the speed is lower.
Cost index is the ratio of time-related costs to fuel-related costs. In climb it is fuel related costs that are going to predominate and when CI is 0 you are going for minimum fuel, maximum range.
Up to you to say what you mean by best climb but there is not that much in it (joke! It is an Airbus)
(usual caveats to FL330 at 75T MTOW ISA).
CI Fuel kg Time mins Dist nm Final RoC fpm
0 1760 22 150 580
20 1840 23 160 570
40 1900 24 165 550
60 1980 25 175 500
Be kind to donkeys. Be different.