I had difficulty last year when talking with a phone AAgent who, despite my request for almost any fare but Q, reserved an unupgradable Q fare to EZE (yet still told me she was processing the upgrades, which of course didn't clear). When I called back to fix it, the difference between Q and the next fare bucket that was upgradable was pretty small--on the order of $30 or $50--well worth it for the long flight.

-Hayden