I'm not in the least worried about the 4th generation iPad performance, contrary to the iPad mini. One might argue that user experience comes before performance, but I doubt that higher performance is not an additional selling point either way you turn it.
In our house we have the original iPhone, the iPhone4, 4s, 5, and iPad2. And soon the iPad4.
The original iPhone feels sluggish, but the 4s and iPad2 represent rather modest improvement in user experience over the iPhone4, and my iPhone5 is pretty much indistinguishable from the 4s/iPad2, judging from what we do with our devices. Doing the experiment of loading heavy web-sites on all devices, plus my new and running above spec PC, demonstrates that pulling ads from the advertisers and the bandwidth of our miserable 15Mbit/s ADSL swamp the differences in processing ability from the 4s and upwards, where the A4 of the iPhone4 was a factor of two slower on one of the websites (Anandtech, incidentally) than on the PC and iPhone5 (same time). Loading bloated websites is pretty much the only thing that feels slow on our iOS devices, and there's not much Apple can do about it now.
So I'd say that increasing CPU performance at this point is more about creating margins for future applications. There's a value in that, and it is an additional selling point to be sure, but it is up against direct and tangible benefits in battery life, weight and form factors. Personally I doubt that a new killer app that requires oodles of processing power will materialize. PCs have had a decade or so without coming up with anything new that is demanding and which interests a large proportion of users. So even if Apple sees these devices as replacing PCs (and they do), that doesn't really provide any impetus to increase CPU performance in the future much beyond current low end PC levels. They are surprisingly close already.
But replacing PCs is not all these devices are about, which brings us to form factors.
In short of the mini sports only iPodTouch5/iPhone4S performance, I'm not that sure that the sales will reach that easily Apple's own projections and yes that's just me.
I'm sure it will sell well, not primarily due to lower price, but because the size is
much better for mobile use than the original iPad. 66% of the screen area at half the weight and the same battery life is tempting in its own right. Sorry Jony Ive, but the original iPad is too clumsy - and I'm speaking as an enthusiastic owner. (Incidentally, the same goes for cameras for me. Just replaced my FF canon system with an Olympus E-M5, but 500-600g is still just too much to tote around when added to everything else.)
When it comes to mobility, tablets should be compared to cell phones, not portable computers which nobody in their right mind carries around with them all day unless required to do so for job reasons.
So for those who really value portability, the e-book/textbook/school market, et cetera, the iPad mini is simply the superior device. And cheaper.
The larger iPads, which can be more squarely aimed at PC replacement, should get rid of that bulky bezel, and use one like the iPhone5 has. That would make the screen exactly 3cm wider and 4cm higher, or a 11.7-inch screen if that's easier to relate to. That would make the screen area 2.2 times greater than the iPad mini, and would allow the screen resolution to yield more practical utility. Without affecting the overall dimensions, this would also allow a clearer diffentiation between large and small iPads in terms of utility and target uses. All IMHO obviously.
These new ipads are undoubtedly unvealed...errr...unveiled..now just to poop on microsoft's parade with windows rt or whatever the hell it's called this week. A6x twice as fast in graphics makes my heart palpitate with joy - actual performance awaiting to be independently verified of course, but since apple was fairly truthful last time when claiming the A5x was twice as fast as the A5, I expect them to not be lying (more or less anyway) this time as well.