Definitely try for a SDC.
I would check in as early as possible since this affects your priority on the standby list. This does not affect your ability to do a SDC. Even if you can't do a SDC online, I would check with the agent at the airport. Also, you can request that the agent put you on the standby list only for a biz seat. This means you only clear if there is a biz seat available and you keep your (presumably) good economy seat otherwise.