I'm in need of a portable, bus powered external HDD, to backup my 2007 MacBook Pro. It has 160GB of Internal storage, so I'm thinking of going with a 320GB or 500GB HDD. Speed is not of essence. http://eshop.macsales.com/shop/firewire/on-the-go http://eshop.macsales.com/shop/firewire/EliteALmini/eSATA_FW800_FW400_USB As far as I can tell, the only difference between the two is the price, size, and eSATA port. What should I go with?