I will be buying the new 2011 MBA to serve as my primary computer after the refresh. This will be my first mac. I am debating which configuration I should go for. 11" or 13"? With or without external monitor? Which processor speed? Which RAM? I will be using my MBA for moderate usage including watching videos, making presentations, writing papers, browsing the internet, using iphoto. I am looking to spend no more than $1300-$1400 total after educational discount. What would be my best option for configuration?