Well, all I'll say is that it doesn't matter how good the weapons are if you have to spread them over a massive border then the net of protection os either going to be weak or have holes in it.
China has a massive border, it runs past India, Mongolia, part of Russia in the North, and Burma, Vietnam, Thailand and several other smaller countries in the South. It probably over 5000km of border. You'd need a LOT of weaponry to defend that properly.
My thoughts are that a hypothetical war against China would be similar to Iraq, only worse. America could probably win Militarily, America has had more of the 'luxury' of testing it's equipment against Russian counterparts than vice-versa, however, unless America is prepared to use WMD's of some description, any kind of troop movement inside the border would be impossible. It would be a pointless war.
If the reverse were to happen and China attacked the US, once again, unless they were prepared to use WMD's they wouldn't stand a hope. America can certainly defend it's own soil if need be, and wouldn't hesitate to use WMD's in that situation.