The power supply will be fine for your SLI setup.
For a cooler I'd suggest looking into this:http://www.newegg.com/Product/Product.aspx?Item=N82E16835608018
Noctua NH-D14 120mm & 140mm SSO CPU Cooler - $95.99
With an SLI setup it's going to get hot in your case.
The Noctua is one of the best air aftermarket HS/F available.
You won't notice the different between x16 and x8, however make sure you get PCI-E 3.0 if you're going with a 670 and ivy-bridge architecture.
As for your starting question I would go with the Asus Sabertooth.
Best of luck on your new build!