Wow. Thanks everyone for all the responses. I think at this point I'll definitely book the F SYD-BKK (if still possible) and then figure something out on the way back. My reasoning for doing the F trip on the trip home was that I'm willing to endure Y during the day, and also I'd rather save the one-way F at the end instead of doing that first and then having a red-eye flight in Y on the way home.

That said, I'll look at doing a TG or SQ day flights home ... or look at the one way C fares sdorling suggested (you've got PM btw ). BKK-SYD in C isn't bad but I can't use MH miles ... I can do SNG-SYD with SQ and I can dump the miles and get PP$ ... That said, the money I spend on the one-way C tix home could be spent at an aman resort or something. -sigh-

Choices, choices.

That said, thanks so far everyone. At least I can book SYD-BKK in F with peace of mind!