You can run at least 5 GPUs on Z170 but it may require some BIOS setting changes. I had a lot of kernel panics, boot failures, etc until I enabled 64-bit PCI-e addressing, disabled USB3.1/thunderbolt and forced PCI-e Gen2 on the CPU links and PCI-e Gen1 on the chipset links. YMMV of course as each board is different.