The tv is not a MST. Your macbook does not support 4k 60hz without using MST. It says right on the apple website that MST is required for 60hz.It's attached to a 2014 imac running boot camp. I tried various high speed cables and I have sub sampling on. Also renamed HDMI-1 to PC but no luck.
The card is capable of running 4k @ 60hz see nvidia press released
B) DisplayPort 1.2
DisplayPort can support 4K @ 60Hz using Multi-Stream Transport(MST). The graphics card provides signals for multiple displays but these are multiplexed on a single cable. Computer monitors such as the ASUS PQ321Q 31.5-in 4K 60 Hz Tiled Monitor take input using this format.
NVIDIA GPU support for 4K Resolutions
All GeForce GTX 600 and 700 series GPUs can support 4K resolutions through DisplayPort. The NVIDIA driver automatically detects 4K 60Hz tiled format, so no special user set up is required. In order to power games at this resolution with settings turned up NVIDIA recommends GTX 780 SLI or better.
Some people who have used bootcamp to install windows 10 on the macbook have been able to get it to do higher than 30hz but they had to do so using Nvidia control Panel Custom Res settings. But even then most people couldn't get a picture at 60hz they had to lower it.