Not sure how you're planning on paying for the flight but when we recently went to book our flights LHR-BKK-LHR using our 2-4-1 we were lucky enough to get a pretty switched on agent who suggested an alternative for pretty much the same avios wise. Now doing LHR-HKG as our 1st First ( independent bookings in between as voucher flights all need to be on BA metal which can't be done) then home in Club BKK-LHR. Cost us 193,000 avios and I think just over £1050.
Gives us a 4 day jaunt in Hong Kong before pushing on to Thailand adding another stamp nin the passports ( and if I can convince the good lady regarding the massive price difference between CX and the Thai' carriers then hopefully access to the CX lounges at HKG). Not sure if it would be of interest but we jumped at the chance to indulge in the 1st experience for I think less than 20k avios difference.
The 773s on the outbound are also newer so it would only mean having the 772 on the way back. Like others above I've heard mixed reviews about the 772s on the route and decided that whichever camp is right making the best of what it is is the way to go. Push comes to shove i'll knock back a few ( sensibly of course) and get my head down day flight or not.