IMO, we already know what the PCB looks like for the iPhone, iPad, AppleTV, and all the other Apple kit thanks to iFixit. The PCB's don't indicate which version they are for. We may see A5X now, but when iFixit tears it down it may show something else entirely.
The article itself sounds like regurgitated guesswork that I made on another day.
A5X, is most likely the A5 with either double ram, double GPU or some other improvement that justifies the change in screen size. Just from a logical point of view, when you have 4 times the number of pixels, you need 4 times the amount of memory. To do a properly setup double-buffer OpenGL display context you need a minimum of 25,165,824 bytes which is up from 6,291,456 bytes needed by the iPad's screen. Then you have to consider higher resolution screen assets. Let's assume that a iPad2 game remastered as a iPad2HD game simply increases the resolution linearly. That means the art assets increase by 4 times without considering compression. So it makes more sense to either quadruple the RAM to sustain the same performance expectations, or to double the RAM and halve the performance expectations. The 25MB frame buffer is the minimum required to use the full resolution at full frame rate. But I think we're hardpressed to put 2GB of RAM in that small of space for now.
LTE, I haven't actually checked what VZ and AT&T use, but I figure the first generation LTE networks likely don't overlap enough to have seamless coverage. Voice isn't used on the iPad (though it could be) but I refer you to how LTE is an all-IP network:
http://en.wikipedia.org/wiki/3GPP_Long_Term_Evolution
This means that the circuit switched voice used on the 2G networks can't hand over to LTE. So if you start a voice call in 2G, and enter LTE space, you are in fact staying on the 2G network. When you end that call, your phone can then seek out a LTE network for data, but if you decide to place a call, it has to fall back to the 3G network if the LTE network has no voice provisioning. Current LTE devices operate in this CSFB mode, which is why each device needs to support it's own 2G network still. As LTE coverage also isn't yet seamless, 2/2.5/3/3.5G network fallback is required, as Verizon would probably cry bloody murder if they had to pay one cent to AT&T for roaming.