I've owned 212K for a month now, and I received a 301K some days ago.
Initially I did a close comparison on display quality and camera. I used a exact same nandroid of Android 4.2.2 with CM10.1, and I flashed factory 4.2.2 images for both before restoring the nandroid. So the software should be quite comparable.
Display: In general, there is no major differences. When compared side-to-side, the 212K was a tiny bit brighter at maximum brightness, but that was pretty much the only difference I noticed. There seemed to be no difference in color reproduction.
Camera: I took a few simultaneous test shots side-by-side, and the 301K image was always tiny bit warmer. Whites were noticeably whiter with 212K. The detail quality e.g. shooting something that had written text was almost identical. I would probably prefer the 212K camera due to the fact that I liked the whites more, but in the end they were enough identical that I don't really care.
Power & volume rockers: on my 212K basically my power button is too stiff. You have to press it quite hard and there is no clear button feedback when it activates. I don't really like it, although it's a good thing it's not too loose... like the volume rocker in my 212K. It makes creaky noise when adjusting, and it wobbles quite a lot sideways. On 301K the power button feels much more natural. There's a button press feedback clearly indicating when it's activated, albeit I'm not sure whether it's going to get looser and creaky in time. The volume rocker on 301K feels really good as well, but time will tell whether it will loosen up as well. These button quality differences could simply be the variation in build quality in all revisions and not really something directly related to these two revisions.
For both of my units 212K and 301K I don't have any light bleed, any earpiece buzz, yellow tint, extra rattle (both has similar rattle which is the normal camera focus mechanism related), and both units are sturdy in general meaning no creaky sounds in any parts of the back or display.