Already I've learned several things from this excercise:

1. Even on Latitude fares, a change fee "may apply*" (though none do on this fare)



2. There are no Tango fares offered on this route
3. The Tango+ changes fees on this route are higher than I expected at $250 (though most people likely would not be able to figure out the actual change fee, using ExpertFlyer for example)
4. This Tango+ fare can be cancelled, even if you no-show, for a $300 penalty
5. On this route, both fares incur the same $412 fuel penalty
6. Even with a $280 change fee (including 12% taxes) you can still make 11 changes with money left over (almost 12 changes in fact) compared to the Latitude fare
7. Latitude avoids the $100 same day change fee, allows preferred seats without charge, reduces the lounge access fee from $50 to $25 and saves $10 on the LHR Arrivals Lounge fee ($55 instead of $65) -- that's potentially a $415 savings (If you have status that maximum savings would only be $200.)

and

8. Picking dates this far in the future significantly delays the evaluation of consequences of changes closer to the flight dates
9. Picking dates in the special travel season of Christmas might be distorting the results