With all the options the "unicorn" system throws in (Gigabyte R9 390 OR MSI GTX 970), it seems to be a waste of horsepower to throw a 1080p monitor in the mix.
I'd encourage more of a 1440p monitor, (I use 2x Asus MX27AQ, which look beautiful). I'd start out with something 1440 that is cheaper, like a ASUS PB258Q.
I've seen a couple monoprice 4k monitors (http://www.monoprice.com/product?p_id=12156) and they look great, and a 970 has more than enough horsepower to run something like that with WoW. WoW looks great at 2560 x 1400 or 3840 X 2160.