I'm taking JFK-HKG as well but in march, and from what I've read on here, it seems that the earlier flight (841), will have a smaller load because of its early departure- not that it really matters in J.

but imo its kinda hard to sleep on a 9am flight, since after all, you did get up not too long ago.. but thats not flight related. Airplane wise, they're both the same bird.

If you want to arrive with minimal jetlag - take the 889 which stops in YVR but adds 4 hrs to the flight time.