I can experience some internet speed problem in BJ too, with some differences.
If we consider the VyprVPN servers in Japan and South Korea have the best pings possible from China (around 70 ms), we have these values almost only in the morning. In the afternoon, evening and night before 2am, the ping values are more often near 150ms.
But I think it's not a problem with the chinese internet inside the country. At the same time, very famous chinese websites continue to answer with ping lower than 20ms.
Perhaps it's more a problem with the gateway to access internet outside China, as more people want to use it.
If we do a traceroute to a foreign website, we can see the ping value becomes high just before to leave China. Because of the GF?
Some foreign websites don't go thru the GF, just like usa.gov, always with a very low ping.
A question to myself (and to staff perhaps): how is it possible to have a ping so low on Japan and South Korea?