My comment wasn't so much about comparing speeds as it was about how irritating it is to find a place to connect. Though, your point is on-topic, so it's all good.

As a foreigner, using a net cafe in either country will probably require you give a scan of your passport/some ID and/or give an address. There's not always a non-smoking area, but if one is already familiar with Japan and China, that shouldn't be too surprising. Moreover, if you're staying at a hotel they've got a scan of your passport anyway, but it's more that some people don't like carrying valuables around.

Free wi-fi seems more prevalent in China than in Japan, though with Toyoko Inns (a Japanese chain) finally offering it, perhaps other places will follow. Though, it's a bit disappointing that at PEK, you have to again use your passport number (or at SHA I think, your phone number- not as big of a deal) to get access. At the same time, random hotel lobbies dotted throughout China have been auspicious wi-fi finds, whereas at Japanese "business" hotels this is almost unheard of.

显而易见, just a few BMB observations.