Turino writes: "Furthermore, you'd have great difficulty getting through airport customs if you decide to exit the country early without sorting out your Z visa first, as your residence permit would still be in date."

Sorry ?, why would the OP have difficulty getting past the airport authorities because of an IN date Residents Permit ? That's plain nonsense.
A Residents Permit is a multi-entry and exit type of 'visa' which allows the holder to pass in and out of China as often as he/she likes while it is valid. Sure, a problem would arise if the person was leaving with an OUT of date RP which would result in a fine, or arriving with an OUT of date RP and no other current permission to enter in the form of another L , F or Z visa.

Think a little deeper before giving advice that can mislead the unwary.