Seems like lately many people have asked for op-up. I would say if you are going to the US, and really want an op-up pretty bad, you should stick with two ports: LAX and JFK. I've been monitoring them through ExpertFlyer and was amazed how LAX flights are mostly sold out in Y all the time. Amazing. With that kind of demand I'm surprise CX isn't adding more planes to this port. Europe is regressing, maybe it's time to divert one of the 773ER to LAX. JFK has 5 flights daily but usually a couple of the flights will be sold out on a regular basis as well. The 10:30 a.m. leaving JFK seems to be a locked for sold out every flight.

Regardless of where you are, even if you want to go to Miami. If you want op-up that badly, fly to LAX then take connection to Miami. Remember, you need to pick flights that have a high chance of sold-out Y possibility before you can even dream of op-up.