Graphics card upgrade;

I currently have in my PC set up a "PNY NVIDIA Quadro K2000D 2GB Professional Video Card".
32GB Corsair Vengeance Pro 2400MHz DDR3 Memory.
Intel Core i7 4930K 6-cored Processor 3.4GHz (Overclocked to up to 4.5GHz)
Now running Windows 10. (after advice from Chillblast who built the PC)

My main use for this PC has been photo editing (from RAW images) and HD video editing.

I would however like to play some video games occasionally.
I tried playing "Watch Dogs" recently but I think the graphics card couldn't keep up with the frame rate at my max resolution on my main monitor (I have 3 but only one is 4K).
I am also looking at getting some "flight simulator software"
I've had recommended to me the following cards:

NVIDIA GeForce GTX 970 4GB Graphics Card
or,
NVIDIA GeForce GTX 980 4GB Graphics Card
or (v.expensive),
NVIDIA GeForce GTX 980 Ti 6GB Graphics Card.

Does anyone have any recommendations based on the above? Please bear in mind I still use photoshop,adobe software, and my nikon software for editing my RAW images and HD video.

Any advice appreciated.

Graphics card upgrade;