How fast is a MacBook Air when it's powered by an Intel Core i7 processor? Now that we've posted performance reports for the standard-configuration MacBook Airs, it was time to turn our attention to testing the optional, build-to-order (BTO) configurations of Apple's latest line of ultra-portable computers.

The brains of the mid-2011 MacBook Airs are ultra-low-voltage Intel Core i5 processors: in the 11-inch model it runs at 1.6GHz, and in the 13-inch model it's 1.7GHz. Macworld Lab ordered both an 11-inch and a 13-inch MacBook Air with faster 1.8GHz Core i7 processors. Upgrading the 11-inch 128GB model to use the Core i7 processor will cost you $150.