Sorry to be a bore and get serious again, but...
Here's something that I would like to throw into the mix:
Flying a COST INDEX is not about minimizing costs, or choosing the most cost effective way to fly. My understanding is that it makes estimating the cost of a flight more predictable. It gives an index (a factor, or a multiplier) for the bean counters to multiply the seat-kms flown.
So, it basically allows for more accurate profit/loss predictions (for the ops guys and the shareholders), which makes it easier to run the business.
For the CI concept to be used effectively, there should be a specific CI for each route and A/C type on that route. What say? Ideas?
Going back to the original post, OPEN DES's flight in post 8 is theoretically the best (while remaining legal)assuming that ATC and traffic would not interfere with your flight profile.
One more thing: You could do away with taxiing altogether though, and simply be towed to and from the runway!
e-taxi and other such systems might actually become a reality sooner than we think!