Your Chinese bank account can handle wire transfers to any international bank account, but you need to provide the documentation. As a foreigner, you need to show proof that the money was legally earned and taxed in China. This can be provided by your employer's HR, or your CPA if you're a business owner. Chinese citizens can also transfer up to 50k USD per year with much less hassle.
Wire transfer is good for large amounts of money (from about 1000 USD up), because it is generally a flat rate of about 150 RMB per transfer.
The fees are for using the SWIFT system, and will be charged whether or not you open an account with a sister branch abroad. A Bank of China account overseas is, for all intents and purposes, the same as having an account with any foreign bank. There's no advantage there.
Simply pulling the money out at an overseas ATM from your Chinese bank card can actually be quite cheap. I just pulled 1000 USD in the states the other day, and between the fees and exchange rate, it cost me about 70 kuai. I've heard of people mailing a bank card home to friends or relatives to withdraw money using this method. Note that there is theoretically a limit of 100k CNY a year for this method, regardless of citizenship or employment status.
I haven't tried Paypal or Moneygram, but every legal method in China will be subject either to the 100k CNY annual limit, or the same documentation requirements described above. It really just comes down to cost and convenience.