There is rather mixed opinion about the harringbone layout on CX's J - narrow seats, compact and coffin-like for some, and hard to look out of the windows (although on over-night flights that's not such an issue perhaps).
BA's NGCW seats on the upper deck of the 747 is really quite a nice and private cabin w/o being cramped (tho not sure if CX's UD is comparable).
Not sure if you have OW status... if you do you may have access to CX's lounges at HKG with a BA J boarding pass too.