The 1060 isn't able to SLI, so there's no way to go at that direction.
Get the 1070Ti if the price is good, otherwise the 1080.
Nevertheless, if you own a 1080p 60Hz monitor you won't notice the difference.
Also, if changing the in-game settings isn't doing anything to your games performance, perhaps you have a bottleneck in your system.
Nevertheless, two 1060 is a no-go.