Thank you all for the contributions.
In the end - I stuck with the upper deck - my first experience with the new bedding (really not sure of the point of that seat cover thing) and it turns out I'm a heavier sleeper than I give myself credit for. According to the crew - they tried to wake me at 50 minutes to landing with a cup of tea and despite giving me a shake I didn't move.
It was pretty quiet even on the UD - not too much noise from anywhere. So I was happy with my choice. But I agree with orbitmic - the empty cabin thing is far rarer and I was very tempted.