I've done this route several times with different routings each time. I expect that it depends a lot on winds, avoiding weather, etc. Perhaps I can lure Jumbodriver over here for some input. I'll send him a PM and we'll see.
Not really much I can add. Rule of thumb is that the prevailing winds at altitude are from the west with strong jetstreams in the 30-55 degree latitude band. These move seasonally and daily so what is good one day may not be good the next. Here
http://www.gcmap.com/mapui?P=HKG-JFK...K&MS=wls&DU=mi you'll see that the great circle track is pretty much straight over the poles. As the northern latitudes rarely have strong winds it may be better to pick up a 150 kt tailwind across the pacific for 8 hrs which is worth 1200nm of extra distance. So whilst HKG-YVR-JFK looks much longer
http://www.gcmap.com/mapui?P=HKG-JFK...K&MS=wls&DU=mi, in reality it could be an hour shorter (only 770 extra miles).
SIN- E Coast is interesting from a prevailing winds point of view as it is not far off halfway around the world. What often happens is they fly eastbound the whole way, so SIN-NYC will go over the pacific/poles, NYC-SIN is often flown trans atlantic and through Europe/Russia if theres a nice strong jetstream.
http://www.gcmap.com/mapui?P=HKG-JFK...K&MS=wls&DU=mi. Any way being within 7-900 nm of the great circle.