As for earlier suggestions to use cheap $60 motherboards....... DONT .
AMD's next generation of processors is going to be released in a few weeks . If you buy a cheap mb now you cut off any chance of future upgrades .Buy a 970 chip set board and you have the core of a system that will last for 5 + years
Unless the sabertooth has features you know you need you wind up just paying more and not getting extra performance
Most people who plan to add a second graphics card never do . By the time you need the extra graphics power then there's always another newer generation of more powerful cards available and you are better off selling the one you have and replacing it completely . Its always worked that way for me , anyway , so I stopped even considering an SLI upgrade.
You definitely wont need to consider any gpu upgrade until you get a 1080p monitor , and even then a 6870 games really well