I have 2 PCs here. One is a i7-6800 with an OpenGL video card, and one is a i7-4770 with a GTX980. Both are running M.2, 32GB RAM, no overclocking.

On Max settings, the i7-6800 scores 4900, and the i7-4770 scores 11800.
On Standard (Laptop) settings, i7-6800 scores 10700, and the i7-4770 scores 15500.

Based on this, the system specs you listed, and the component hierarchies at TomsHardware...

http://www.tomshardware.com/reviews/...rchy,4312.html
http://www.tomshardware.com/reviews/...rchy,4388.html

...I think you'll get the best performance boost by upgrading your CPU. However, you can do no wrong with an upgrade of either at this point.