If I might make a slightly off topic response here mr. eldest.
I get the feeling from you that keeping certain files safe is very important to you, hence the raid 1 and nas backup.
I didn't know if you were aware of this but if there are any critcal files you dont use often (like pictures or divorce papers :P) you should probably but them on writable dvd's or bluray as they are not mechanical means of storage and you can put them in a fireproof safe.
I say this becuase I do it myself, any files that I actually care about are on a dvd in a safe, if lightning struck right now I wouldnt care.
Hope this helps. oh and on topic, I would choose the spinpoint f4, for somereason even at 5400rpm they certainly scream in performance, and since seagate just bought them (the hdd division of samsung) the f4s are going to be the last of truely samsung product, which are fabulous for reliablilty.