Apple calls the processor in the newer iPad as A5X indicating that it is NOT a major processor upgrade. This indeed is a the case. While the GPU undergoes a substantial improvement from 2 cores to 4 cores the CPU number of cores stays same – the 2012 iPad is still a dual core processors.
While the GPU upgrade was a must, in light of the 4x increase in the display pixel count, processor requirement increase is not as urgent. The dual core Cortex A9 is still good enough. Apple had two choices – either go with the quad core Cortext A9 or the newer dual core Cortex A15. The Cortext A15 is still very new and it is unreasonable to assume that Apple would have met the March 2012 release deadline, if it would have liked to bring in the Cortex A15. The Texas Instruments was the first to come up with a working silicon based upon Cortex A15.
All this sums up to the fact that we will have to wait till 2013 to see the Cortex A15 based solution in iPad. In most likelyhood, Apple will call it A6, which will truly indicate that it is a real processor upgrade.
But Apple did double the memory from 512 MB to 1 GB, which was, kind of essential, given the heavy data transfer required by the 4x increase in the graphics pixel count.
In a nutshell, we should see little or no gain in the processor performance, while the GPU and memory look at doubling the capacity – and both these resources go on to improve to improve the retina display.