I am considering buying a refurbished MacBook Air, either 2011 or 2012, in either case, 256GB SSD. I will use it principally for email, notetaking and web browsing. Since the 2011 refurbs are cheaper, I am leaning in that direction. Aside from CPU speed, is there any downside to the 2011 model compared to 2012? Does 4GB seem to be adequate? Thanks in advance for your advice.