If you can, I recommend waiting at least a few more months before deciding which 4k screen to purchase. We know that at least ASUS is planning to come out with a 39" 4k screen (using the same VA panel as the $700 39" Seiki), and so it's probably worth waiting to see how that comes out (Q1 2014 is the supposed release for that).
However, if you really want the nicer panel quality and don't like the thought of a VA panel, I am unaware of anything that is likely to really usurp the IGZO PQ321Q in the next year. In that case, so long as you have the cash and know you're probably paying at least a $1500 early adopter premium, the PQ321Q is a good purchase if you have the GPU muscle to power it
I personally have a hard time justifying >$1500 for any screen, so I'm holding out