What should my next upgrade be?

[Conner1320]

My current gaming setup is:
Corsair CX600M PSU
Asus Z97-E motherboard
Intel i7 4790k 4.0GHz
Nividia gtx 970 wind force
8gb ram
2x1tb HDD
What should my next upgrade be?(besides a SSD)

 

[jwcrellin]

Maybe a gtx 1080, the price is about to drop next week to under $500. How good is your 550W power supply? Also another 8gb of ram wouldn't hurt but i'd hesitate to invest more in ddr3.