Thank you Michael Dell. You just made my Christmas 2014 a better one. Your sales organization sold me a P2815Q in November 2014 for $399 / free over night delivery. This purchase will likely go down as one of the best computer monitor purchases of all time. DISCLAIMER: Not a gamer or a graphic designer so display speed and true color were not a top requirement nor extensively tested.
Once the right cable and settings are set, this colors displayed and 24 bit images are incredible. Even tried it out with youtube and it passed my growing test.
Mac Pro (mid 2013) OS X Yosemite 10.10.1
Purchase a Mini DisplayPort to Mini DisplayPort cable from Apple(not the 1.2 version and not the Thunderbolt cable). Plug it into the only MniDisplay Port on the Monitor and plug the other end into one of the six MacPro MiniDisplayPort port. Make sure you don't overload one of the three MiniDisplayPort buses by plugging your MiniDisplayPort monitor cable into the same bus as your (screaming fast) external storage device. This yields ---> Dell P2815Q --> 3840 x 2160 @ 30Hz. This monitor will never goto 60HZ no matter what you try.
I have a Retina Display Macbook Pro and iPad Air with Retina Display and the displayed image on the P2815Q is near equal.
Set Sharpness 40, Brightness 28 and contrast 65 on the monitor. Use RGB Color. DDC/CI Enabled.
On the Mac Pro, goto Settings --> Display use Scaled and select the 1920 x 1080 resolution.
On the Mac Pro, goto Settings --> Accessibility and leave Differ w/o Color, Increase Contrast and Reduce Transparency UNCHECKED. Reduce the Size of the Mouse Pointer. Set the Display Contrast to the 1st quadrant out of 6.
If you want to color calibrate your monitor for more advanced color capabilities, go for it but right out of the box, it works if all you want is more real estate at a greatly reduced price.
Was this easy to figure out? No and really all Apple Support could do was to confirm the details of the technical specifications of all the different cables(HDMI to HDMI/Mini DisplayPort to Mini DisplayPort/ HDMI to Mini DisplayPort / ThunderBolt to ThunderBolt) and explain the Thunderbolt port on the Mac Pro is backward to the Mini DisplayPort port.Now they can provide feedback on which settings to tweak to fix the washed out image problem. It is not a limitation of the monitor but a fining the needle in the haystack problem. In the long run, this meant learning about pairing a HD 4K Monitor to the Mac Pro including creating a custom scaled resolution using SwitchResX which was not really required but fun.
Now just in time for Black Friday.