When configuring a MacBook Air, I noticed that to upgrade to the 1.8 GHz processor cost $270. I passed, thinking that the difference between 1.6 GHz and 1.8 GHz would be too marginal to warrant the cost. Now comes all the second guessing, of course. My concern is that the 1.6 GHz option would perform more slowly than the processor in the MacBook I'm typing this on, which has a 1.83 GHz Intel Core Duo. I mainly use notebooks for lightweight activities, if that matters. Do you think the difference between the 1.6 and 1.8 GHz options is substantial enough for the money and for favorable comparison to my Rev. A MacBook? Thanks for your help.