If you are compressing a video file or encoding an audio file in iTunes, the 2.4GHz i5 will be much faster than the 2.13Ghz Core 2 Duo. For Application loading, booting, navigating your machine, and surfing the web the MacBook Air will be faster due to its hardwired Flash NAND-based storage, it can access data faster and cache files faster, but it cannot crunch numbers and data faster. For pure CPU-intensive tasks like converting or compressing audio or video, which can take hours, you would be much better off with an i5 or i7 because the little Core 2 Duo is going to leave you waiting. But still it's an excellent machine for light use and browsing the web.