Here are my specs. I am currently trying to decide what gpu to upgrade to. I have no preference here just looking for ideas. my budget is 300 to 400$. here are my specs.
Intel core i7-4770k
Asus Z97-A
gtx660 ti
corsair vengeance lp 4gb (2x4gb) ddr3-1600 memory
corsair obsidian 800d
ATX 600w
Depending on your current PSU, I would recommend an R9 390.
If you really want to stick with nVidia, grab a 970. You might be able to get them right at $270 to $300 with the sales coming up soon.
With the left over money, you could put it towards an SSD of 240GB to 256GB or perhaps another matching 8GB kit of RAM.
Wait until january, prices will fall. Then grab a r9 390 or gtx 970.
my psu is atx 600w
If you dont plan oc it should be fine.