I think that you can technically standy-by for an earlier domestic flight, JFK-SFO or LAX, but you may not get an upgrade? I do not believe it is within the rules to stand-by for an earlier international flight, but that is based solely on my recollection of previous posts on the subject. I have tried this (standing by for an earlier int'l flight) twice without success, although one time I think the agent might have accommodated me if business class had not already check in full? If you are sufficiently worried, and you have the time, then by all means go to the airport and kindly ask. Nothing to lose, except some sleep I guess? (Note that the upgrade situation on 891/837/853 might not be any better than 801?)