Okay I think I found a way to solve my specific problem (which is that my monitor loses signal, but the game still runs in the background). Previously I had to reduce the core clock to 920MHz.
Now I found that reducing both the core voltage and aux voltage to -44 (I keep the Power Limit at +50), I can play at stock clocks. I have tested BF4, Assassin's Creed 4 and Batman Arkham Origins and no loss of signal to my monitor yet.
Does this mean it's definitely a driver problem for me and not hardware? I really don't want to rma this card.
Its a driver issue. Dont RMA just YET.