I currently have a Late '09 13" Macbook Pro 2.2ghz upgraded to 4gb of RAM and a 320gb 7200rpm HDD. I have some extra cash, and have decided that I want to upgrade one of these to either 8gb of RAM or a Momentus XT 500gb HDD. I do a lot of work in Photoshop and Illustrator, and was wondering which would be a better upgrade, as I can only do one. The Momentus is $115, while the RAM is $180. Thanks.