This and this combined (note different settings in use per chart) would suggest that a 950 or 370 is basically "good enough" for your needs, though they'd not too future-proof, but I think it wouldn't be too much of a problem seeing as both cards are still somewhat faster than a PS4.
The 970 and 390 would last you a long time, given that they're significantly faster than an Xbox One or PS4. Really, they're kind of like 3 Xbox Ones duct taped together, and perhaps more, if you overclock them, especially the 970.
Just asking: what's your CPU and PSU? Play CPU-intensive games (which sometimes might not be obvious?)
(Also, please, try for the MSI Gaming 970 instead of the Zotac if you can help it.)
I have an AMD Phenom 964 4x and a 650w psu. I know that the cpu needs an update but I'm waiting until I get a new Mobo. I haven't decided if I want an AMD processor or an Intel processor. I've been told that my gpu needs to be upgraded sooner than my cpu/ Mobo.
Also, I try to play blops 3 with little success. I want to get rise of the tomb raider and quantum break soon.
The 370 is not even a significant performance upgrade over a 6970, believe it or not, although it would have much more compatibility in modern games.
If you must upgrade now (I don't blame you with your 5+ year old GPU) get the 390. It will likely have better longevity than the 970, since that is a chief concern of yours. There are several models cheaper than that though:
http://pcpartpicker.com/parts/video-card/#c=311&sort=a8&page=1
Thanks for the suggestions!