There's also the Black and Comodoro issue as well. There seems to be a lot of them on those routes and they get priority on the seats up front in the upgrade system. One of the things the LAN computers actually seem to track is how many of them are still not checked in and/or haven't asked for upgrade since they've got an unlimited number of upgrades for themselves. Also every time I've been on either of the LIM-LAX flights J has been full even when the system showed seats available up front earlier in the day. Also remember that all you'll have is a request (unless you're using kms) until you get to the airport and maybe the gate.

Good luck!