I'm not entirely convinced it's worth the 8K.
There're only 2 rows of 2x2.
The seats are better than Y, but it's the old business seats. You do get better service and a 3-course meal. IFE comes in the form of personal video players.
I was in the first row of Y on QF47 a few months ago, so I was able to observe what's going on up there. BTW, my flight was 100% full, even in J. Although I said I don't think it's worth it, I did find it hard in Y, but that was probably because I just got off a 24hr flight from LHR in J. I'd imagine I'd still find it hard if I was in J.