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On the 2013 Mac Pro
The Dell UP2414Q was tested on the 2013 Mac Pro by connecting it as a 3rd display, in addition to a NEC PA302W and NEC PA301W (dual 2560 X 1600 30-inch displays). That’s a lot of screen real estate, but the 2013 Mac Pro handled it with aplomb.
Handy trick if a 4K display is to be used for its resolution with no concern for text size, configure it at native 3840 X 2160 resolution; it reduces the size of any web browser or similar stuff around images (no need for pixel doubling / scaling). See further below for details.
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.
To set to native 3840 X 2160 resolution, option-click onto see the extra choices.