just a heads up... the Delta fly HKG-NRT, and their business class is priced at HK$5300 return all in, which is same as Economy CX to HKG-HND. For comparison, CX J is priced 4x richer at about 20k HKD. Obviously got restriction like no date changes etc but I think that's a serious alternative to burning 50000 x 4 = 200k Asiamiles which is probably enough for HKG-JFK in first.
the price is always available provided subclass S is available.
I'm loyal CX customer (or used to be) but my next trip to Tokyo i'm going the Delta option. If your dates are fixed, you might want to consider this as your alternative.