Well thanks all for the thoughts
I personally tested both the cards and landed up on Rx 580 because, I opened the same files in lumion using 2 cards and Checked that
1. MSI GTX 1060 6gb oc V2 - was giving 14-15 fps and vram 4700 of 6100 mb was free
2. Asus dual Rx 580 oc 8gb - was giving 19-20 fps and 6700 of 8100 vram was free
Even though MSI GTX 1060 has boost of 1760 mhz and Rx 580 has boost 1350 mhz, somewhere I could say Rx 580 was better
MSI furmark stress gave 78c max
Rx 580 furmark stress gave 72c max
So Rx 580 I bought over GTX 1060 and am happy