Best price/performance GPU is still GTX970 even after GTX980 price cut.
GTX980 is only 10-15% faster than GTX970 but about 100-200 bucks more expensive.
GTX980's price can not justify the extra 0.5GB extra VRAM too.
Both GTX980 and GTX970 will struggle on Witcher 3 @1440p if you aim ultra settings with all effects on plus mods like E3FX.
You can also try to OC your GTX970 to reach GTX980 stock performance. (luck is involved here)
any 980 will suffice perfectly.. if thats too much and if u wanna save a few bucks then get a 390X..
The 390X is not a very good price : performance GPU.
However the R9 290X that has been drastically reduced in price is an outstanding option because of it's excellent price : performance and there are rumors that after DX 12 comes out the R9 290X performance will drastically be improved.
i completely agree KKAW but he was already implying that hes shooting around 500 and the 390X competes with that card... but i would say a gtx 970 is the most viable option...