i wouldn't trust that psu to deliver clean and stable power. Based on what i've learned from the psu experts here on ocn, i'm willing to bet that it is a junker that is to be avoided. Sure, it has a pretty face, but that's probably about where it ends. In other words, it's more than likely not a safe power supply to use when you're going to be investing your money in nice computer parts.
Here are others within that price range that will have all the power you could ever need to power a system that has two gtx 470s in sli:
don't be afraid of the rosewill brand name or the sentey brand name. These 2 units are recommended units! The rosewill green series is not "awesome", but it's good enough that psu experts do recommend it. However, the sentey golden steel power series is almost as good as the seasonic x-series!
So if you can buy one of these, then your system will be much better off.
If you're not comfortable with 650w units (although, they have quite enough power), then here are some units with larger capacities:
i guarantee that all of these units are way better than psus like the xion, and i guarantee that they will all have enough power to power a system that has two gtx 470s in sli.