New pc

If you're willing to spend $1000 euro on upgrading follow my steps.

I upgraded to a GTX 1080 8gb from a GTX 960 like what you have and I also upgraded from a i5-4460 to an i7-8700k and I can run every AAA game in high or ultra settings without any lag at all.

Then with the money you have left over look into getting 16gb of ram most likely from Corsair since they're pretty high quality.