I'm not a good friend of that controller card. Always is better the SATA III and USB 3.0 that comes from the manufacturer by default. But is a good option.
Now, if u still preferring the SLI over Crossfire, is better go with an Intel rig that support both multiples GPUs and have more mobos with better options.
Bear in mind that the 470 in performance is between the 5850 and 5870, in SLI the performance is better on the 470. The 5850 is a little more expensive, but use less power and works with less heat that the 470.