Get Dell UP2414Q at B&H Photo.
As shown below, dual 30-inch 2560 X 1600 displays are accompanied by the 3840 X 2160 Dell UP2414Q at right. The NEC PA302W has the menu bar at center. This configuration worked with no issue whatsoever on the 2013 Mac Pro.
The stunning clarity of a 4K display is hardly to be believed, whether in Photoshop or with the UltraHD 4K images in diglloyd publications. That’s 8.3 megapixels displayed for the eye to enjoy, fully half of the total resolution of many digital cameras! It’s like looking at an 8 X 10 'chrome'.