What to upgrade next?

Miyconst

Honorable
That depends on what you use the PC for.

If for gaming then I see those options:

- Buy Samsung 850 Evo 500gb SSD to install games.
- Sell your GTX 970 and buy a GTX 1070.
- Buy another GTX 970 for SLI, but your PSU is a bit weak for such load.

If for video encoding or other intensive work:

- Sell your CPU and get an i7-6700k.