Personally I would do what I did and get an 11" Air with the i7 2.0 processor, and 8GB of ram. The thing hauls big time. I was in the same boat as you not to long ago, i couldn't decide if i wanted a bigger laptop for more power to phase out my mac mini at work instead of having an Air (mid 2011 model) and the mini and going back and forth. I thought I could combine them into one world and be set. So I got a 15" macbook pro, used it for a day or two and returned it. Then when the new 2012 Airs came out I just maxed out the 11" version. It's the ultimate portable machine and it has a lot of power. I take this thing everywhere and it is probably the best laptop I have ever owned.
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The i5 isn't a major drawback to me (though I think 4GB of RAM is getting to be the lower-limit of acceptable for multitasking at all) since I use the Mac Pro and Mac Mini Server for any "heavier" work. The size and weight of the 11" MBA is just perfect for a laptop/secondary computer.