Both CPUs and Mainboards have VT-d and VT-x But the
Z170-A have x16/x8 - PCI-E: 2 x PCIe 3.0/2.0 x16 (x16 or dual x8)
Z170-WS have x16/x16 - PCI-E: 4 x PCIe 3.0/2.0 x16 (single at x16, dual at x16/x16 mode, triple at x16/x8/x8 mode or quad x8/x8/x8/x8 mode)
or works GPU Passthrough with x16/x8 and x16/x16? but i think on the Z170 WS it runs both gpu with max speed.
The board matters only becuse of the drivers available. You'll never going to saturate a x8 PCIe connection with any GPU ever made till now. What matters in the first place to be able to do GPU passthrough is the CPU and both the CPU you chose are capable of it. The WS board has a PLX chip that multplies the CPU PCIe lanes because both CPUs just have 16 lanes so migh even lead to worst performance. To recap things you're good with both boards.
You can't use v5 CPU's on the Z170 chipset. Intel restricted the microcode to C series chipsets. The v1, v2, and v3 E3 Xeons did not have this restriction. You will need a C232 or C236 based board in order to use a Xeon E3 v5 processor.
I'm not familiar with your rendering software or rendering in general. Do you benefit from having more than 6 cores/12 threads? That being said the 2620 v4 is clocked so low that the 6800K would probably still outperform it.
For sure if you drop GPU passthrough it would remove much of the potential hassle.
Looks like 6700k supports VT-d
If later you decide to try passthough it probably will still work. You just might need to patch the kernel.
when passthrough not work ok then not and i play not the ea or Ubi games that not my problem, thats the problem from UBI and EA when they are not make an game for linux.
I Use Autodesk Maya and MODO for 3D modelling under Manjaro Linux ^^