FWIW, in this use-case the limit is the wifi or more likey your internet connection speed. You don't really need blazing disk read/write speeds for your "Dropbox clone" - if you can read and write data as fast as your adsl connection goes - anything more is "wasted". As a general purpose file server though - yeah, a 'Pi isn't going to stream multiple HD videos to all 4 bedrooms on your home network.