so i am looking to buy one of the new imacs and i noticed that the 20-inch 2.4 ghz model has the same graphics card (ATI Radeon HD 2600 PRO) and same vram (256MB of GDDR3) as the 24-inch, 2.8ghz model. which of these two has "better graphics." does the larger screen of the 2.8 ghz model mean that it will render images slower and play video games at with fewer frames per second? does the additional .4 ghz of clock speed in the 2.8 ghz model improve its graphics at all?