Right, so DP 1.3 which supports "32.4 Gbit/s with the new HBR3... a 5K display (5120 × 2880) at 60 Hz with 30 bit/px RGB color" is enough.
The UP2715K, only support dual link DP 1.2/HBR2, which was a bit of a PITA on my machine because nvidia's board partners don't always do a good job of describing which ports on the back of the card can be used for dual link.
8bit 4k at 120Hz:
10bit 5k at 60Hz: