I googled the screen flickering issue while overclocking with two monitors. I used After Burner and setup two profiles. The first I bumped the voltage to 1220(was 1160) and left the clocks at default, then made it my 2d profile. For the second profile I set the voltage at 1220, bumped my clocks where I want them and saved it as my 3d profile. What I read said the base voltage is so low it doesn't handle any tinkering with the clocks, and a slight vcore bump fixes the issue. So far it seemed to work.
Intel I7-4770K, 8gb G.Skill DDR3 1600C9, MSI Z87M, AMD 5870 1GB, 240gb SSD + 1TB WD Black, Cooler Master Hyper 212 EVo