Do you still get the problem if you set your cpu to stock speed?
I had a similar issue which was solved by lowering my ram speed. Sli can be tricky to get working in my experience, try downloading a gpu monitoring tool (i use evga precision) to check both cards are getting balanced usage.
I had bad tearing problems playing Just Cause 2 with Sli, set Nvidia control panel to single display performance mode, it fixed the problem.
Hope that helps