Right - the OP just needs to make it clear when he gets to FRA that he doesn't want to take the earlier flight if it means giving up his confirmed C seats and sitting in Y on the earlier flight. IME, standing by from an upgraded ticket almost universally results in a downgrade to your original class, as (I *think*) if you standby for an earlier flight and try for an upgrade, you're put on the DM list along with everyone else. Can anyone confirm that?