FlyerBeek - thanks for the suggestion. I was reading the AA site left to right and was assuming B was higher than Y, but with azmmza 's numbers I will definitely look into B.

The rationale is that I need about 2500 miles on AA before end of year. Plenty of options to get them, but I hate taking unnecessary flights and using up 6-8 good hours on a mileage run if there is a way to get them on the flight I already have. I am pretty sure they will let me up the ticket, but not sure they will let me upgrade just one portion to B without upgrading the entire itinerary? In particular the LAX-HKG segment because I am connecting through to HKG-BKK. I know logically they should take more money from me, but a good portion of fare terms are not logical to begin with, so you never know? But given the difference above, even upping the entire trip may not be that much - and perhaps worth it (about 4000 additional EQM to start the new year).

And christep - thanks also. My original question did read like I was asking about a flight upgrade, so based on your original response I changed the wording to be more accurate to what I am looking for.