Mac Mini Server 2011 and Thunderbolt Dock

Hello everyone,

I just purchased a 2011 Mac Mini Server (id 5,3 quad core i7 2.0ghz). It has 8gb ram and I just installed two ssds in the machine: 256gb for the OS and 500gb for data.

I'm using the Belkin Thunderbolt Express Dock (F4U55) and I'm having issues connecting to my LG 27UD68-W 4k Monitor. I know I'll only get 2560 x 1440 but when I connect the monitor through the dock, I get input lag. It works fine via HDMI. Can I not use an external display through the thunderbolt dock with this Mac Mini? Also, my thunderbolt cable is firmware version 1.0.16. Should I purchase a newer thunderbolt 2 cable? Is there even a difference?

Thanks