I know apple has underclocked the GPUs. But how much of a difference in Mhz in a gpu's clock speed will there be a noticeable difference in performance? And many people have said it was too weak to fully use the 512mb potential. Is it possible that when it is overclocked, it will be powerful enough to use it? Will OC-ing the card void warranty? Will apple know if you did if you reset it's performance to default?