Did any of you try a Displayport to HDMI adapter to connect your PC with the TV, and could you get 2160P@60 ?
Here is an example of such an adapter which supposedly works well:
www .club-3d.com/index.php/products/reader.en/product/displayport-12-to-hdmi-20-uhd-active-adapter.html
Here you can read some reviews on Amazon:
Amazon.de:Kundenrezensionen: Club 3D DisplayPort 1.2 auf HDMI 2.0 4K60Hz UHD Aktiver Adapter
My Dell E7440 laptop and even my Dell 7130 tablet can connect up to 2160P@30. The bottleneck is the HDMI 1.4 because of the bandwidth limitation.