I'm currently running low on HDD space on my 2x750GB NAS (DNS-323) & am considering upgrading to 2x1000GB Samsung Ecogreen 5400RPM HDD's.
The existing 7200rpm HDD's are a pair of Samsung 7200rpm HDD's I had that were spare from upgrades, and they produce bugger all heat compared to the WD's and Seagate's HDD's I've owned ... but when I pull them out of the NAS, they're quite warm - the NAS only has a little 40mm fan at the rear. Pitiful
I figure that the 5400rpm HDD's should produce a little less heat, and hence live a little longer.
The NAS devices seems limited to approximately 20MB/s across the gigabit ethernet, and the 5400RPM hdd's should easily do 60MB/s sustained.
The NAS basically streams Bluray rips (upto 30Mb/s = approx 4MB/s) or low bitrate avi's to my PS3, located beside it.
On rare occasions, it may be playing an avi from the NAS, while I dump files on it from somewhere else on the network.
The access delay across gigabit network basically renders any difference in access times between the 7200rpm & 5400rpm drive completely irrelevant.