I've got four on there right now - no issues. Ordered another 2 vegas last night so we'll see if I can get 6 running, seems the more you add the more issues people have.

Be aware this board requires three additional power connectors. 2 molex and 1 sata and supposedly three different cables. Though, from what I've read you can skip the extra sata, and use one molex to power both additional molex's on the board. That kinda caught me off guard.