I have my Octo 2.8 up an purring. I want to add another drive to the stock 500GB that I configured. I picked out the brand...a server grade WD. Question is what size HDD to get. 500GB or 750GB. I have no plans to run RAID config on it as of yet, but I want to make this drive for storing media files. What is a better future investment? The 500 at 100 bucks or the 750 at nearly double that? Sorry for the Noob question, but I have no idea how many files of what size. Thought I would poll the audience. Thank you to the best Mac Forum around!!!