While Mxhawthy´s suggestion is good, I feel it should have been a 980TI card or a 970 - the 980 sits weirdly in between those 2 cards.
GTX 970 is great for 1080p (Full HD). So unless you plan to play in higher resolution, you don´t really need more. GTX 970 will play 1440p (2K) as well.
I've put this together for you. It's a really good PC, which will play any games at highest settings in 60FPS at 1080p. It will also run games very well in 4K if you have a 4K monitor.
While Mxhawthy´s suggestion is good, I feel it should have been a 980TI card or a 970 - the 980 sits weirdly in between those 2 cards.
GTX 970 is great for 1080p (Full HD). So unless you plan to play in higher resolution, you don´t really need more. GTX 970 will play 1440p (2K) as well.