Comparison video on YouTube 1060 6gb vs 1060 3gb. and the difference was about 7-12% lower on current top titles with average 45-65fps ultra settings in 1080p. https://www.youtube.com/watch?v=fYNigmB6sWY
Graphics cards not for upgrade if you have latest generation gaming card, but for 3-4 generation old!
I have returned 970gtx 4gb in favour if this. strix was not as good as I hoped for.