JFK-NRT is a great segment to do in UA C. As other posters have noted, UA C is quite comfy for lounging. The JFK-NRT flight leaves late morning so you are ready to be awake for the bulk of the flight (for which the UA C seats are perfect).

One of the other posters suggested re-routing. Not a terrible idea to HKG, but definitely do not re-route via ORD, go via SFO. The total duration going that way is about the same as via ORD (both of which are a little shorter than via NRT) but you get the DVD players in P.S. C to SF and then do not have to worry about running out of movies on the long sector. Additionally, routing via SFO puts you in to HKG a few hours earlier (you also leave a few hours earlier). If I do not have to be in Tokyo my preference from NYC to HKG (and v.v.) is actually via SFO (for the reasons I noted).