Your findings are really spot on. They are very useful.
I took my i5-4690K processor on a H97 motherboard to Best Buy to plug a DP 1.2 cable, from the PC, to a Panasonic AX800U 4K TV. I adjusted the DP settings on the AX800U to SST.
I achieved on WQHD 2560x1440@60HZ. I was so close to 3840x2160@60Hz.
What kind of 5th generation processor for a desktop, will allow me to achieve 3840x2160@60Hz?