I have a 2009 13" MBP that is running kind of slow, even though I upgraded it with an SSD a few years back. I'm thinking of getting one of new MB Air models. Deciding on which tier. I really don't use my laptop that much. When I do, I usually just use it for web browsing, word processing, storing photos, and syncing with iTunes. Nothing crazy. Is the base model good enough for me or should I get the mid-tier model?