I have a single GTX 1080 MSI Gaming X with a 165hz 1440p monitor. In games like CSGO, Dota 2, Pay Day 2, LoL, etc. I get 300 fps. In games like Witcher 3, Thief, Rust, Skyrim, etc. I get 90 - 120 fps.
I honestly dont notice a difference when playing at 90-120 fps vs 300 fps. My monitor also...