I would go with the Asrock 970 Extreme 4, Supports SLI/XFire. Price pretty close to the same. ( $109.99 )
Possibly change the PSU to Corsair TX650 V2 ~$65 after rebates. OR XFX Core Pro 650W $65 after rebates or XFX Core Pro 550W $55 after rebates. Or possibly make sure you have a molex to 6 pin PCIe adaptor as the Graphics card needs 2 connectors and the PSU only comes with one.
The above all come with 2 minimum. XFX 650W with 4.
Other than that looks like a pretty solid build to me.
$700 budget? I would go with an Intel i5-2500K instead of any CPU from AMD at that budget. Admittedly the quad core Phenom IIs shouldn't bottleneck a single 6870 so it shouldn't be a problem but still, upgrading the graphics might need a CPU upgrade too.
Also, a single molex connector is not safely enough for a 6 pin PCIe connector. If you need a molex to PCIe adapter then you should get one that uses two or three molex connectors. There is a reason that we use PCIe connectors and not molex on video cards anymore, molex isn't intended to handle the amount of current that PCIe connectors do.
It is better to just have a power supply thast has enough PCIe connectors for your video card anyway but if it doesn't then don't just convert a single molex into a 6 pin or even worse an 8 pin PCIe connector.
I would like to know how a $50 Cooler Master (before a $20 rebate) looks like Seasonic quality??? You can't be serious! The power supply that you chose is not going to provide enough power for the 6870 which requires a 550w psu , so you should get a real Seasonic psu;