The worst part of any trip to the other side of the world is getting there and getting back. China, in particular, doesn't offer much flexibility in that regard. For the most part, no matter where you are going in China, you need to fly into and out of Beijing. There are some flights into Shanghai and you could start at Hong Kong, but those are even longer flights, with even more connections from SMF. Since I have no desire to put up with more than 20 hours of flight and airport time in one shot, I always plan to spend the last night and most of a day in Beijing, try to catch up with friends and/or just walk around.
