FWIW, I flew ORD-HKG a few weeks ago, left on a Wednesday and came back one day into the Chinese Lunar New Year. On the way out there were a number of empty C seats, coach 80% full, and on the way back the plane was only about 40% full in C and Y (don't know about F).

I bought this ticket with only a few days advance notice and was able to easily get a confirmed upgrade upon purchase.