Debian Testing GTX750 4k@50/60Hz HDMI

my Graphics card is a ZOTAC GTX750OC.
I use an LG TV 40UB800V which ist 3840x2160@60 capable but only has HDMI (2.0) Ports.
I tried a 5m passive DP->HDMI cable but it only allows 1920y1080@60Hz in Windows and Linux.
I tried a “good” HDMI (2.0capable) cable which allows 3840x2160@60 in Windows 7.
But i can’t get the nvidia driver in Debian to switch to 60Hz or 50Hz.
It always shows 30,25 or 24Hz.
A Modeline generated with “cvt” isn’t working.
Read out the Windows setting with “mi_setup.exe” only shows 1920x1080 modelines.
How can i modify xorg.conf to get this working ?

I changed my card to brand new gtx960 with hdmi 2.0.
it runs 3840x2160@60hz per hdmi connection in windows 7 but only 30hz in linux.
i installed newest x86_64 driver today.
how to get this work ?