Alright, so you think my choice of hdds is ok?
The greens don't perform as well, but they use less power (which is why they're "more efficient) and run cooler. The cooler operation makes them an excellent choice for external enclosures or if you're trying to stuff a LOT of drives internally into a case.
Something most people overlook is reliability ratings. Certain models of the WD Blue drives (including the 500GB model) have a higher reliability specification (less than 1 unrecoverable error per 10^15 bits read) than the Black drives (1 per 10^14 bits read).
Black for system
, since its faster and blue for storage
, since it's more reliable.