How come? The platform is more efficient than any other competitor to begin with. A5 has yet to be beaten, let alone A5X. When the ipad3 hits the market, how many other products will actually be on the market that feature a next gen/better CPU? Or a next gen/better GPU?
I say practically because a lot of that extra horse power will be necessary just to drive the higher resolution display. Also, synthetic benchmarks don't always translate into real world performance and in many cases additional GPU power doesn't amount to anything.
What I'm most interested in seeing are the webpage load speed tests and other tests that Anand usually includes in tablet reviews. If we know the clock speed of the A5X, we can probably deduce how much of a performance bump iOS can get from GPU acceleration, assuming it hasn't already topped out in that regard.
The A5X is definitely interesting, but as I mentioned in another thread, the A6 is really what interests me, as the A5X is not really suitable for the next iPhone. I'm assuming from the name that the A5X is still using Cortex A9 ARM cores, but depending on when Apple releases the next iPhone, the A6 may very well be a Cortex A15 design and use newer PowerVR graphics. It's even possible that Apple's SoC design has been inverted, such that the iPhone will see the newer chip design, and the iPad will get the X version of the SoC that adds additional graphics.