I think this is possible only if all GPU's are installed into x16 slots, but I have not heard about the existence of motherboards with 6x PCIE x16 slots.
The best result I saw using I7-8700K and 1x1060 was 500KH @PCIEx16, 420KH @PCIEx4 and 230KH @PCIEx1.
I7-8700K. 1060@PCIEx16 + 1060@PCIEx4:
0-509.1 1-412.5 Total: 921.6 H/s 2018/05/30 11:36:13 0 - Yay, solution found!
G3258. 1070@PCIEx16 + 1060@PCIEx1:
0-492.3 1-223.7 Total: 716.0 H/s 2018/05/30 13:37:15 1 - Yay, solution found!
I7-2600: 1060@PCIEx16 + 1060@PCIEx1 +1060@PCIEx4
0-350.3 1-235.5 2-306.7 Total: 892.5 H/s 2018/05/30 13:38:43 0 - Yay, solution found!