Quite a few years ago but I have been in one of the twin seats on this variant to the USA. From what I remember it was bearable.

Yes it's near the back so I would recommend taking a good pair of ear plugs and if there is any turbulence then you will feel it right down the back as well as being last off the aircraft. Overall though not a bad trade off though for being in the twin seats with no one next to you and hopefully those 7 hours will whizz by including the time you get airborne, meal service, perhaps a film or documentary and then just 3 hours ish 'to go'

The last hour/40 minutes to go then there can be a little queue nearby.

As far as economy goes it's OK at best, it is what it is.