Deciding between 7200rpm 500gb and 5400rpm 750gb drive in the new 2.2ghz model. I def don't need the 750gb, so it's more a question of speed vs noise. I will use the computer for audio recording. Recording to an external fw drive. When I put a 7200rpm into my old 13" it was definitely louder than he stock 5400rpm. Not terrible, but slightly annoying in a quiet recording environment. What would you go with?