Hello all,
Just to add a different thought here, I've read in a few places that some storage experts are shying away from the idea of always getting exact matched disks for RAID sets.
If you get all the same disks, they have presumably been made all in the same factory at roughly the same time, under the same conditions. This MAY mean that whatever quirks or defects that result in failure later on could be in all the drives, which raises the probability that more than one will fail at the same time.
Best way to mitigate this risk is to get very different drives - different manufacturers even. But try to match performance specs as best you can.