I'm considering selling my 11" Mid 2011 Air and upgrading the screen. I'll be getting a 2013 13" Air. Performance and feature wise is it worth it? I do have to give up clock speed. The 13" Mid 2013 Air is 1.3Ghz and my 2011 is 1.6Ghz both will have 4 gigs of ram and 128 Gig SSD'd.