And seeing that you are adding a new graphics card to your rig, let me say that the new Nvidias - the 1070 is what I picked up - rock. I was playing with shadows on medium, no DOF, no motion blur and pretty much everything else on ultra; my 280x 3GB kept around 40 ~ 60 FPS @ 1440p/96Hz.
Now, with the 1070, "nightmare" cache size and lighting is opened up (8GB of VRAM) as well as TSSAA 8TX being viable and oh my...a very different game. 80 ~ 120 FPS and it really looks amazing; a very noticeable difference in visual fidelity and smooth as silk. IdTech 6 really shines when it has the horsepower to show off.
So, if you can afford it, get at least the 1070. It only draws 150w but outperforms the 980Ti pretty much across the board. I haven't even started thinking about overclocking yet, which apparently yields a significant boost. I don't think Polaris will touch these cards, so unless you want to wait until Vega in 2017, these are the cards to beat.