Thanks to everyone who contributed to this discussion. Since our tickets included both PEK and HKG, it seems to make much more sense to fly to XIY from PEK. Hainan flies at the right time for us, so that decision is made.
Now, for another question from someone who really doesn’t know anything about China. People here brought up the idea of Guangzhou, known to my generation as Canton. I was there once with friends from Macau, but all we did was have a big party in a hotel restaurant on the former concession island and then head straight back to Macau. Those of us with Brazilian passports didn’t even bother getting China visas and the border police didn’t seem to care. There is apparently a nice train from Hung Hom to Guangzhou. Would that make a pleasant day trip, or does Guangzhou have lots of sights that might make it desirable to stay overnight?