best stick with default setting that Intel recommends
RAID5 performance using software raid (Intel raid) is poor at best...
also aslong as your aware it only protects against a single drive failure - wont help for deletion, corruption or virus's and if one drive fails most likely the others being the same age and ware will also fail at the same time
Intel recommends Stripe Size 64 kB, but has no recommendation for Block Size on partitions created. I'm pretty sure it doesn't matter if the Stripe Size and Block Size are different ...but if anyone can confirm or deny, that would be nice.
As for backup, I'm only using RAID5 for redundancy, not backup.