Hey I came across your thread the other day looking for a possible fix for my own problem of low FPS with my GTX 970. If you already fixed your issue then ignore this but if not then another thread I came upon mentioned using this program:
http://www.guru3d.com/files-details/display-driver-uninstaller-download.html
Basically what it does is completely uninstalls your drivers and all registry files in windows. Then you just reinstall the latest Nvidia driver like you just reinstalled a fresh copy of windows. I just did this earlier today and was able to fix my problem of low FPS . Before the ill gotten gains update my FPS was 60-70 with geforce experience settings and then after the update until now my FPS has been 30-40 no matter what settings I changed. After using the program and reinstalling the latest Nividia driver my FPS is back up to 60-70 with geforce experience recommended settings. I think this could probably help you. Even if it does not a fresh install of drivers never hurts. Good luck and hopefully it works.