Max voltage input to microcontroller
You shouldn't use the input protection circuits as the normal means of limiting input voltage on a pin.  They are there only as an emergency protective device.

I haven't looked at the PIC datasheet, but from other IC specs, I think that the MAX values you mention will be found in a table headed "Absolute Maximum Ratings" or words to that effect.  

Atmel's Absolute Maximum Ratings table includes the following note:


  "Stresses beyond those listed under “Absolute  Maximum Ratings” may
  cause permanent damage to the device. This is a stress rating only and
  functional operation of the device at these or  other conditions
  beyond those indicated in the  operational sections of this
  specification is not  implied. Exposure to absolute maximum rating 
  conditions for extended periods may affect  device reliability"


I would use a voltage divider and a 5 volt zener diode to limit the voltage applied to the IC to the recommended values.