4K display/monitor

All this talk of 4K displays and Mac Pros has me really envious. I was looking around and saw this 39-inch 4K TV for only $500, and started thinking that it would be a great monitor. I currently have an iMac (late 2012) but unfortunately, unlike the rMBP or the new Mac Pro, doesn't have an HDMI 1.4 port (which Apple says can drive 4K). However, Apple also says that you can drive 4K with a compatible Thunderbolt to HDMI adapter (would this work)? It's a very confusing mess and the root of the problem is that HDMI 1.4 only supports 3840x2160 up to 30 Hz (which then becomes more confusing as some say HDMI 2.0 can be enabled with a software update). Do you think that a computer is usable at 30 Hz (albeit also at 4K)? The screen real estate sounds amazing especially for only $499. (Think about it - you can get 2 4K displays for the price of a 1440p Thunderbolt display! That's 16588800 pixels vs. 3686400! 4.5x the pixels!).

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TL;DR: It all boils down to 30 Hz. Do you think it's a usable refresh rate for a computer?