I was going to ask this same thing. I'm currently using a motherboard that has difficulty running 3.
So far the only two MB's I use are the Asrock H81 Pro BTC and the Asrock Z97 Anniversary - and with both I have them working fine with 6 cards, but I've been eyeballing this MSI board because 7 boards would be pretty cool.
About the only anecdotal thing I can say is that guy who was selling that prebuilt FUEL160 system was using this this motherboard (I tracked down this board based on the pictures), and was running 8 cards (splitting on of the PCI-e slots into two)...