I would agree with trying the schedule change tactic and getting a confirmed change with no cost. Otherwise, check seatcounter.com 4 hours before the flight. If it's pretty full, I would suggest paying the $50 for confirmed standby. Twice recently I have tried to risk it and save the $50 and ended up spending an extra 2 hours at the bar. There's also a slight risk that the flight could have some open seats but if things are hectic or they're behind at all, they'll leave before processing all the standbys.