... I've been re-reading the thread.... noticed you mentioned that you intend to go with a raid 5... anyway, a while back I was reading the merits of raid 0 + 1 over raid 5 at storagereview...
I'm not sure where over there it was, but surely its something to look into... there may have been significant threads on the topic here too as I could have sworn seeing someone here ramble on how raid 0 + 1 is so much better
EDIT:
StorageReview Raid Info Note that raid 0 + 1 is aparantly called raid 01 (and simularily 1 + 0 is called raid 10). While the link is to the sumary comparison table, it might be a good idea to read the individual writeups on raid 5 & raid 01/10 as they contain aditional usefull info (particularily on how raid 10 is better in some ways that raid 01)