http://www.guru3d.com/articles_pages/fallout_4_pc_graphics_performance_benchmark_review,7.html
Fallout 4 still needs optimization, but according to their tests, the 770 got 72, the 970 got 88. Only 16FPS for $250+. Turn down some of your settings for now, wait for better Nvidia drivers and some game updates to see if it gets better. Lots of people are having FPS issues with fallout and staying at 60fps with better GPU's than the 970. Outside scenes, etc can bring a system to a crawl.
What is the rest of your hardware?