No, HK not noticeably better than Japan, and Japan is only a little better than the US.
You biggest problem is that everything going into mainland China goes through the Great Firewall, which tends to slow stuff down (both lag and latency). (Outgoing data is faster, which I suspect means they don't really monitor it as actively).
The only way around TGF is to host your site in a mainland datacenter, probably getting a .cn address, and * definitely* complying with China's internet regulations.
Google does this, but it can't serve results from a mainland center (as it doesn't want to follow mainland regulations), so it gives you a link to results served by google.hk (which I think is hosted in Hong Kong, but you can probably host a .hk address in the US or Japan, since HK is pretty lax with regulations).
If you want fast mainland connections, you need a mainland datacenter, probably a .cn address, and to do that you need to follow Chinese regulations.
I don't know about North/South. Possibly some stuff is done by provincial governments. Certain zones (like Shenzhen), and people (or companies) with permission might be able to get unfiltered internet. Maybe there's two Great Firewalls, and you need two centers to get inside both. I'm not an expert.
But I'm 99% sure that HK datacenters will have the same obstacles (re TGF) that non-Chinese datacenters have.
As itsnotvalid has pointed out, some sites are best going to the effort of getting a mainland address, simply because it means China will try to work out any issues with you rather than simply banning you. As the paperwork and features are likely to take a while (I'm not an expert, but paperwork always takes time, especially if it's in another language), you might want to start the process before they ban your main site, to avoid service interruptions (and maybe for goodwill - it can't hurt to look like you want to cooperate).
You biggest problem is that everything going into mainland China goes through the Great Firewall, which tends to slow stuff down (both lag and latency). (Outgoing data is faster, which I suspect means they don't really monitor it as actively).
The only way around TGF is to host your site in a mainland datacenter, probably getting a .cn address, and * definitely* complying with China's internet regulations.
Google does this, but it can't serve results from a mainland center (as it doesn't want to follow mainland regulations), so it gives you a link to results served by google.hk (which I think is hosted in Hong Kong, but you can probably host a .hk address in the US or Japan, since HK is pretty lax with regulations).
If you want fast mainland connections, you need a mainland datacenter, probably a .cn address, and to do that you need to follow Chinese regulations.
I don't know about North/South. Possibly some stuff is done by provincial governments. Certain zones (like Shenzhen), and people (or companies) with permission might be able to get unfiltered internet. Maybe there's two Great Firewalls, and you need two centers to get inside both. I'm not an expert.
But I'm 99% sure that HK datacenters will have the same obstacles (re TGF) that non-Chinese datacenters have.
As itsnotvalid has pointed out, some sites are best going to the effort of getting a mainland address, simply because it means China will try to work out any issues with you rather than simply banning you. As the paperwork and features are likely to take a while (I'm not an expert, but paperwork always takes time, especially if it's in another language), you might want to start the process before they ban your main site, to avoid service interruptions (and maybe for goodwill - it can't hurt to look like you want to cooperate).
Also, you can get a CDN (maybe http://en.chinacache.com/index.htm) to cache stuff. I think that would help.