Dual Mini-dp or Thunderbolt for 5k on mid 2015 mbp with Dell UP2715K?

Hi,

Im hoping some other owners of the DELL UP2715K monitor could provide some advice on how to connect it to a Mid2015 Macbook Pro Retina. For some reason I am not able to get my Macbook to recognise the 5k resolution. Currently it is setup so that I have the two Mini-dp to Displayport cables plugged into the two thunderbolt ports but the maximum resolution I seem to be able to achieve is 3840x2160 @ 60hz. I

have tried alternating thunderbolt ports and forcing an edid override (initially to fix the blurry font rendering – still not fixed) but neither solution worked. its starting to be a real bug bear, which wouldn't be as bad (4k is good enough for my work most of the time) if the fonts weren't blurry... In fact trying to fix that is what made me realise I was unable to reach the 5k resolution..

I also use the monitor in 5k mode from my windows box, and from what I can see, it works with out any problems. This has lead me to believe that the monitor is fine and that the problem lies with how I've set it up / am using it with OSX.. After googling and reading a few other posts and articles, my current thinking is that perhaps I need two ThunderBolt cables rather than two Mini-Displayport -> DisplayPort ones..

As you can see, I'm a bit lost as what to try next, so any help or advice would be most appreciated (and awesome).

The monitor and Macbook Pro are set up as follows:

Input Source: DP(5k3k)

Color:

Input Color Format: RGB

Gamma: Mac

Preset Modes: Standard

Aspect Ratio: Wide 16:9

Sharpness: 50

Response Time: Normal

DDC/CI: Enable

Resolution:

3840x2160 @ 60hz

Macbook Pro Retina (15-inch, Mid 2015):

OSX El Capitan 10.11.3

Automatic Graphics Switching: Off