I still maintain that the issue of using 3 copies and a two must match philosophy versus a 2 copies and a XOR CRC approach depends on a number of factors including:

- Absolute level reliability needed, 

- How big of data element packets you
  are dealing with,

- How much time you can afford to do the 
  update.

- And finally how does the required sized 
  EEPROM fit into the cost budget for the
  project.

Mike