I'm in the market for a new laptop. I'm currently considering either a base model 13" rMBP or a similarly priced Air. The retina display is appealing to me, but I'm thinking its not worth it to me. When using the laptop at work it will be hooked up to an external monitor so I won't be using the retina screen. In terms of performance, will there be much difference between the 2.5 i5 of the rMBP and the 2.0 i7 of the air?