I hate using dual PSU. They have always headache. And motherboard that have 6+ pci-e slots are extremely overpriced. I prefer 4/5 gpu rigs. Easy and cheaper to build. Easier to handle the hardware/software problems 
What is your preference for 4/5 gpu board? I know there is a ton of options out there does it really matter or do you take bios into account when picking the ones you have gone with?