You still have to be sure t keep in mind that if you have a core duo at 2.0 Ghz, your computer is not running at 4 Ghz still. In may situations your system will be running at somewhere between 2 and 4Ghz because not all applications will be able to take advantage of both cores. In most cases things like OS X Tiger will take advantage of both, and a few running applications will and a few won't... it is to be expected.