Sli is dead. The 1060 doesn't support sli, you'd need a 1070 or higher, 2070 Super or higher or a 3090.
Gpu's abilities are finally outpacing gaming requirements, especially for 1080p and for a good chunk of games at 1440p, so the necessity for multiple cards has become obsolete to get good fps.
The 1060 is still respectable for 1080p, but it's fps is determined by the cpu, and especially the game code.
Start with ultra, then customize that. Drop viewing distance, lighting affects, nameplates and any other cpu bound settings to medium/low. That'll leave a clear definition between cpu and gpu outputs. Note the fps levels in game. Then drop the settings to medium/low preset. If fps jumps up, then the gpu was struggling at the higher settings and choking the fps output. If fps really didn't move much of any, then it's the cpu that's not supplying the higher frame rates, it's topped out and the gpu isn't an issue.
Cpu low fps output can be anything from trash in temp files to registry settings, ram usage, pagefile usage, temp issues, malware, anything.