The better duration and you can visit some more interesting places popular in China. Explore the mighty Yangtze on a river cruise or shop till you drop in Hong Kong. Try to see the lovely pandas in Chengdu or even join a volunteer propram to get closer to them. Expand your stay in Shanghai to the surrounding water towns or heavenly Suzhou & Hangzhou, or add a short break to breath-taking Mt. Huangshan. Also, don't forget the mysterious Tibet.