A camera outperforming an older one at ISO12800 when examining the .jpg files out of the camera is a very narrow way of looking at image quality. It is misleading to state that the new Sony's have better image quality (full stop) as it is not the case for most other settings. It is not surprising that newer algorithms can clean up an image at high ISO better than the old software/ hardware of the older models.
It's also worth noting that the 5DII only goes up to a native ISO6400. Anything after that is "boosted" in the software rather than direct sensor capture. That in itself will increase noise, in the same way that upping the exposure on the computer will do the same. I had a quick look in Lightroom and of the 61,000 images I have less than 200 using ISO6400 and above, with a large majority of those being test shots to see what various cameras can do (the ISO 120,400 of the 1DIV is not pretty!) so the (super) high ISO performance of a camera is not so important to me, for sports/ concert or other photographers, I am sure it will be useful though.
A lot of the tests are also flawed as they are not making the correct comparison, i.e. the extra crop required from a 5D image to get the same shot from APS-C sensors etc etc. Some get it right, some get it wrong, but it all depends on what point you want to prove.
I have been pixel peeping at various images from the new models that come out, but there is a fair difference in quality when looking at something from full frame or something from an APS-C. It could be argued that the difference at a pixel level makes no difference in practical use, as the majority of images will only be displayed at screen resolution or on a small/ medium print, but the difference is still there.
I would love it if smaller cameras and sensors could beast the full frame models, but they aren't there yet IMHO. One thing is clear though, the next generation of the D700/ 5DII need to pull some heavy punches in order to keep their high price tags justified. Technology is getting better and more affordable by the month!