https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1060/26.html
*GTX1060 matches or beats the GTX980 in general.
As said, the GTX980 may be able to overclock higher but that's likely a small amount. There's other differnces:
a) 6GB vs 4GB (ignore the 3GB 1060)
b) H265/HEVC encode/decode
c) dynamic load balancing (should help future DX12/Vulkan titles a bit)
d) quieter/less heat
e) WARRANTY on GTX980?
f) RESELL value
g) VR support (SMP or Simultaneous Multi Projection can make a huge difference in how well the titles work.
https://www.roadtovr.com/nvidia-explains-pascal-simultaneous-multi-projection-lens-matched-shading-for-vr/
Basically if you can get a GTX980 for a lot cheaper then go for it as the most important thing is VRAM capacity, and 4GB is still plenty for most titles.
*Prices are also screwed up due to cryptomining, BUT, if you wait a while (few months?) we should see EBay etc flooded with used cards for relatively cheap.