I wouldn't worry about "blocking" seats for other couples. There will be many singles on the upper deck based on my experience. I've used 53A and 50B to avoid waking up my neighbour when in need of a toilet break. Noise from the galley is, as others have reported, an issue with 53A. You can however be disturbed (sometimes physically bumped into - ouch) in 50B by fellow pax heading to the washrooms but leaving that aside it is much quieter. I would have recommended this for your partners needs as it is also the shortest route to the washroom and would have allowed you to sit next to her, but I see from The BA Source seat map comments that 50A has a window by the footstool which defeats your looking out the window objective.
So if you don't want your partner disturbed then your non adjacent seat approach might make sense. Or you might put her in 50B and you take 51A.
I think you will enjoy the 380; I have done many sectors to/from HKG on them, and I much prefer it to the (noisy) 777 that also plies that route.