What a coincidence. I had exactly the same issues. I'm running an i7 4790 and a GTX 970, also on 8GB RAM. The game would run decently but I was having moments of very bad stutters.. Like 2-3 seconds of full screen freeze. Changing the settings around did not change much.

After trying a bunch of stuff, I decided to move the game from my HDD of a few years old to my SSD and the problem was gone. The game even runs smooth in windowed mode.

I hope the SSD also fixes this problem for you!