Q:

Motherboard Compatability

The amount of Video Cards a motherboard can support (if using powered risers) is only limited by the number of PCI-E slots, correct? I've found a board (MSI - B250 GAMING M3 ATX LGA1151 Motherboard) that has 2 PCI-E 16x and 4 PCI-E 1x. If I use powered risers there should be no issue right?

A:

Not necessarily correct, though it may be correct in your situation. It appears some people have issues with fully populating the PCI-e slots, though it's unclear whether a BIOS update or reconfiguration would have helped.
I also recently read something on a review site that was testing a motherboard for fun that supported a ridiculous number of PCI-e slots (pretty sure it was more than 10). However, it refused to work when fully populated with AMD cards. All slots were usable when a few nVidia cards were used. Not clear whether this was an OS or hardware limit. Speaking of which, you may also wish to consider OS limits. I seem to recall encountering instances of people running into walls with certain versions of Windows 8 and 5+ GPUs.
I can't say for certain that all motherboards can support as many GPUs as they have PCI-e slots, but I can say that some configurations may involve tofurkey sacrifices and head-banging.
P.S. I'm not endorsing (or discouraging) this particular setup, but you should be aware of things like the potential for fire when dealing with high-power setups and equipment of questionable repute (I'm looking at you, powered risers of unknown origin).

