So I'm considering buying a 2013 MBA (11' model) to use alongside my aging MBP. I'd use the Air mostly for writing and surfing, and the only somewhat demanding software I plan to use is Mekentosj Papers, a PDF archiver/reference manager (I'm an academic). Is the clock speed upgrade from 1.3 to 1.7 worth the £100 it costs? Would I even notice the difference? Cheers.