I could have been a little clearer with my post in retrospect. My point about Cost Index is that, if your Ops Eng people caclulate CI for a specific flight, then varying the CI will vary the Climb speed schedule and hence the Time to height and the Distance to TOC with the obvious impact on Fuel used in the climb etc. Neither everyone uses PBTH contracts, nor do you believe everything a manufacturer or leasing company tells you about performance.