I know it’s rather old, but is the GLX 560 still supposed to work with the nvidia-38x drivers? When Ubuntu (14.04) upgraded me from 375 to 384, the performance dropped to basically nothing, both as a video card and CUDA. I see the same thing with KDE neon (based on Ubuntu 16.04, I believe) and it doesn’t matter if I use the drivers from Ubuntu or download from nvidea. Returning to 375 downloaded from nvidia restores performance.
Here are links to the requested files: