30 Hz is awful. The brightness problem is blow out and bleed. It is "very bright" it is so bright that when doing any sort of calibration the whites bleed on everything. The contrast ratio is good due to the excessive brightness, which means the blacks still suck. Horrible highlights and horrible shadows.

The calibration you can do in the OS is limited, as I said, I have two different sets of hardware equipment for calibration and I still couldn't make it less than horrible. The display is just ick (as expected at that price point) -- every color is signifigantly off out of the box, and trying to fix it even with physical calibration devices is a lost cause. You can't get it anywhere near "normal".

I tried the TV against multiple forms of input -- from Windows to OS-X to Ubuntu to QNX(I used to build command center software, which ran on TVs on top of QNX, so I have my own stack that is tested against TVs). From nVidia, to ATI, to Intel. I also tried it as a simple TV (my fallback so I didn't have to sell it) -- it even looked like crap as a TV... even with external upscaling to 4k.

I purchased mine (and used it for about a month before I was able to sell it on Craigslist) just about as soon as you could get one in the US. I doubt any radical changes have taken place since then, I have read of none outside of the price dropping. It is still generally reviewed as a poor TV and worse monitor.

Dells 4k 28" should be available in just a few weeks -- wait for that, don't purchase this lemon.