This is a bit of a complicated question which I tried to research before orfering my new computer late last fall. The answer is less straightforward than it may appear. Core Duo and Core 2 Duo both feature 2 processors on one core. But, the architecture and performance characteristics of these processors are not the same, and they come in a range of clock speeds, the Core Duo having a maximum of 3 GHz and the Core 2 Duo 2.93 GHz. Tests done with Core 2 Duo and Core Duo on Photoshop indicate little performance difference, but the Core Duo - for example a processor such as the Intel Xeon 5160 - lends itself to quad-core upgrading (i.e. 2 processors on two cores yielding a total of 4 processors) whereas the Core 2 Duo (Intel E6800) I think I read does not. However, I have also read that the Core Duo is said not to support 64 bit computing, whereas the Core 2 Duo does. But not many applications - and not Photoshop - support 64 bit computing - yet. Quite a few comparisons and speed tests have been implemented with the various models of these generic processor types on a number of computer technically-oriented websites. You can do a Google search and read the various results. Overall one gets the general impression that performance rates accross a range of processing functions appear to give the Core 2 Duo a small speed advantage, but not clearly so for digital imaging in particular.