I agree with the general sentiments here about the 789 having better cabin air and pressure etc.

However, two notes of caution:

- almost all of the 789 F cabins are scruffy and damaged. The original design of them was not very clever and, although BA seems to have come up with solutions to prevent most of this in future, almost none of the sub fleet has had the required upgrade. So prepare for reading lights hanging off, table lamps that don’t work, scuffed leather surrounds, chipped table etc. All that said, the new 77W seat is notoriously unreliable and I am 280,000 Avios richer thanks to two overnight trips in F where my seat didn’t recline.

- the timings of the earlier flight are better. There is less of a rush to bed time from the crew and having a decent dinner at 8 rather than midnight allows for some time to digest and enjoy a movie before going to bed at a more natural hour. You can also enjoy the evening in Singapore more when you arrive.