Peter...the lack of replies to your question is interesting. I can only assume no one wants to admit to flying long haul economy in case it lowers their street cred or most BAEC Golds on here fly QR J for the cheap tier points.

For the sake of bumping the thread I shall offer you my opinion which I should warn you is worth sod all judging by FT member feedback.
Only the 747 I'm afraid but here goes. I found the upper deck on a long overnight flight was much more enjoyable against a long overnight flight on the lower deck in the middle middle seats. Although my wife thought the middle middle seats were 'great' for a couple.

However my most enjoyable CW flight was to YVR on the lower deck. The wife was in the window seat while I was relegated to the aisle. It was all very relaxed due to the 'holiday feel' which prevailed amongst the passengers and superb cabin crew. A great experience all round.