Really, the only sure RAID array is a backed-up-and-verified one.

The only piece of information you missed is that RAID 6 came about -- RAID 5 with two parity stripes -- because there was an anomaly in the statistical failure rates WRT to partition size that exacerbated secondary failures whilst re-bulding from a disk failure. Which RAID 6 only puts off, not solves. Which is why a decent vendor will recommend a complete rebuild-and-restore from the controller up once a disk has died and been replaced...

Wade.