I am deciding between a 500GB or 1TB HDD for external storage. I own a mbp15 with 4GB of memory. I'm using the laptop for simple internet, email, WORD, Excel, Powerpoint, Keynote, etc. The only thing that I think would take up a lot of space would be music and maybe a few downloaded tv shows. Would 500GB be enough or did you find that 500GB filled up real fast. Thanks.