I believe you were the one who asked me question on my posts regarding the 767-400ERX this past week (or maybe it was the end of last week). The biggest obstacle facing Boeing's sales efforts to 767-300ER operators of the 767-400ER has been the range penalty when compared to the 767-300ER. That's why Boeing's product development people have been examining a follow on for some time now. I recall one discussion in the U.S. Airways competition in which the 767-400ER didn't quite have all the range needed on some routes (Rome maybe?). Therefore, if you make the -300 and -400 interchangeable on all routes by having the ranges similar, you don't have to worry which routes have to use the longer range aircraft so you can more efficiently meet demand.