I'm looking at getting a 20'' iMac, but am torn on whether the difference between the ATI graphics cards available on the two I'm looking at will make that much of a difference: 1. ATI Radeon HD 2400 XT with 128MB memory 2. ATI Radeon HD 2600 Pro with 256MB memory Does anyone know if the performance between the two is drastically different? The 2600 version of the iMac has a 2.4 GHz processor while the 2400 one has a 2.0 GHz processor. It would be cool if Apple provided the option to choose the 2.0 GHz processor with the Radeon HD 2600 Pro graphics card, but they don't.