I used only Asrock motherboards. Extreme 3 and 4 work well with 4 GPUs. But now you can purchase the Asrock BTC series which are made for mining. Those can handle 5 even 6 GPUs at once if you manage to set them up correctly in Windows 8.
Is there an AMD equivalent to Asrock BTC series? Is there another company that makes something similar to Asrock BTC series? I like the two molex power connectors for the PCI-Express.