I also had a bad/fake 20mhz resonator.

I then tried some Farnell ones and decent crystals all worked ok, even at 96mhz.

The board actually worked in the car at 96mhz but that is overspec (12mhz) for the 10mhz MCP2515 CAN controllers SPI so I dialled the PIC back to 80mhz for reliability and (10mhz SPI)

So a decent increase in speed over 64mhz at zero cost so far.

Now back to the other thread to do some code speed optimisation before I add additional functionality with my extra free time.