iMovie doesn't exactly render that fast, as it's not a professional application meant to render as fast and effectively as possible. With 2 processors, you'll be able to use one for rendering and have the other to use another App. At school with the 1.25 GHz eMacs some of the kids edit and it slows down to a miserable crawl when transitions are rendering. Having 2 CPU's is a huuuuuge advantage. Also, up the RAM as much as you can.