So what did Apple do with that extra space it added to the A6? It went to an extra graphics processing core of which there are now 4 on the chip, up from the 3 on the A6. While the CPU size remains the same on the two, the GPU cores are larger on the A6X. Not only that, but when looked at through a microscope, the 4 GPU cores are divided into 9 sub-cores, two sets of 4 and 1 central sub-core.
One analyst says this could be done for better parallel processing, or for a faster clock speed. Either way, he says that graphic speed will be blazing on the fourth-generation iPad thanks to the PowerVR SGX 554 GPU in the A6X. The chip also has double the SDRAM interface of the A6. All together, it sounds like Apple has really beefed up its full-sized tablet in time for the holiday shopping season.
source: Chipworks via AppleInsider