At my airline (It's not really mine, I just work for them),
Sector specific Cost Index (CI) is used.
Advice to pilots is by company bulletin (through Flight Operations Web page), periodically updated as maintenance / variable overhead / fuel prices vary.
It's not on the Nav Log, or Computer generated Flight Plan (CFP). The CFP uses CI=150 which is MUCH higher than actual CIs used. We love that, we inevitabely 'make' fuel on each sector. Typical CI is in the range 85 to 88, although the 'full' CI=150 is standard on some sectors due to schedule / connection problems. Also, beyond a particular threshold, the CI is bumped up to 150 if late on schedule. Minimum CI=50 (wait for this to change as fuel prices rise further).
The calculation is performed in the traditional Cost Index calculation technique. As speeds increase, flight times, and therefore airframe / maintenance cost decreases. As speeds increase above Maximum Range Cruise, fuel cost increases. Where the decreasing airframe cost crosses the increasing fuel cost on a graph, lies the optimum Cost speed for the sector.
SOPs are to fly the published sector-specific CI, except as mentioned above (schedule etc.).
Everyone in our outfit knows that a fixed CI does lead to the same old set of speeds from day to day. CI=150 was used regularly as standard until a year or so ago, everyone knew the speeds from memory, and are aware in the 'new era' that these speeds now vary somewhat.
SR71, I guess that with a call-sign like yours, your personal CI is 999.