The hit on the wallet was not small at all unfortunately, but after having it for just over a year, I'm very very happy I did decide to push the boat out.
1080p just looks so blocky
You need a 980 to run 4k (or two 970's). When I got mine in dec 2014 the 980 had only just come out, if I was getting now I'd buy a 980ti.
This is the monitor I got,
https://www.overclockers.co.uk/samsung-u28d590d-28-3840x2160-tn-4k-60hz-1ms-gaming-widescreen-led-monitor-black-mo-204-sa.html
It was £500ish when i got it, and another £500ish for the overclocked 980.
GFX card,
https://www.overclockers.co.uk/gigabyte-geforce-gtx-980-g1-gaming-4096mb-gddr5-pci-express-graphics-card-gx-148-gi.html
I'm seeing my monitor for around $500 in the US now, after a quick search.
I did think about getting the 32inch until I saw the price, when I bought my 28inch, the 32inch was £1600, screw that!
Good thing about having a card that can run 4k, is that it will be able to do VR as well, I'm hearing that they're saying a 980 recommended as min for VR as well.....