I got my Zotac Mini last week and did some tests: with my current rig, 3DMark score increased from 3601 points with the GTX 970 to 3993 points with the GTX 1060. More importantly, the upgrade improved the performance of Elite: Dangerous in VR! I didn't quite reach constant 90 FPS in all situations I compared the cards in (hangar, station interior, planet surface, space, conflict zone), but on average got 15% more FPS! And on top of that, some issues where I had the impression that the head tracking of the Oculus Rift got wonky when I was on the bridge of large ships like the Cutter and Clipper within starports, probably because of the limited amount of VRAM of the 970 (4GB), got completely resolved by the switch to the new 6GB card!
In addition, the Zotac Mini is - like the name implies - very small and extremely easy to fit into my PC case, much easier indeed than the huge MSI 970 card was! Its also even quitter than its predecessor, up to the point where I'd call it nearly completely silent, even when the GPU is running with 100% usage!
And last but not least, the new card needs even less power than the already very power efficient 970, reducing the TDP from 145 watts with the 970 to just 120 watts (tops!) with the 1060!
The really great thing about all this, though, is, that this nice upgrade did - like I hoped - turn out to be quite cheap for me in the end, because I was indeed able to sell my used GTX 970 for 230€ the other day on Ebay!
With the Zotacs price being around 280€, the smoother ED VR performance and reduced power consumption of the card did cost me only 50€ in the end!
So, one happy consumer here! Thanks everyone for your thoughtful advice to not upgrade from the 970 to the 1060, but I am happy I didn't follow it
p), the upgrade did exactly get me the modest improvement of performance I wanted, for the little price I was willing to pay! 
In addition, the Zotac Mini is - like the name implies - very small and extremely easy to fit into my PC case, much easier indeed than the huge MSI 970 card was! Its also even quitter than its predecessor, up to the point where I'd call it nearly completely silent, even when the GPU is running with 100% usage!
And last but not least, the new card needs even less power than the already very power efficient 970, reducing the TDP from 145 watts with the 970 to just 120 watts (tops!) with the 1060!
The really great thing about all this, though, is, that this nice upgrade did - like I hoped - turn out to be quite cheap for me in the end, because I was indeed able to sell my used GTX 970 for 230€ the other day on Ebay!
So, one happy consumer here! Thanks everyone for your thoughtful advice to not upgrade from the 970 to the 1060, but I am happy I didn't follow it