With Ethash, the GTX gives 24.x MHs compared to 27 of the RX (without the BIOS mod).
You'll only get 24.x MH/s from 1060s if they come with Samsung memory. And these days it's becoming a rare sight, more and more of them come with Hynix or Micron. If you get Hynix, then they're basically useless for ETH mining, because at ~ 20 MH/s max you're better off just mining other coins with them.
I have Zotac cards that come with Samsung memory. And Zotac is cheaper than most other brands.