I've been looking at a Western Digital - My Passport Essential 500GB External USB 3.0/2.0 Portable Hard Drive. What is the speed of this drive (5,400 or 7,400 RPM) and does it make a big difference? I have looked everywhere for this spec. My primary purpose is save my finished audio and video projects to an external drive. Would this be a well recommended drive, since I would like to have two, to be on the safer side?