Mate,
I did the commute from HK to syd during training, and it sucked some serious balls! And that's a 9 hour commute on basically the same time zone!
Getting seats was never really an issue...I think there were 3 flights per day at the time (A330). Mind you, it was always a little nerve racking waiting on the flights on the way back. Thankfully the Syd check-in staff are much nicer than the trolls in honkers.
The big problem was getting the time to get home. Somehow (and this is my experience...not necessarily that of everyone) i seemed to get an event every 4-5 days, pretty well making the commute unrealistic. (1 day used to get home, plan to get back in HK a day early to have some fat if I miss a flight, a day back...leaves me with 1-2 days home) So anyway...after not seeing wifey and the ankle-biters for 3 months....well..you get the picture!
I'm 744, so that might make a difference if you're scarebus or 777, but i don't know. All I do know is that given the chance to do it all again.....i wouldn't. No amount of beer washes away the taste of balls.