There is no thing like "best fps rate for a monitor". Like TJ Hooker said, it depends on the games.
I upgraded to 165hz 1440p monitor with G-Sync and use it to play games with my GTX 1070. I don't need the higher fps/hz for most games, so I can dial down some settings and don't mind that. Crysis 3 in example runs this way at 70 to 90fps with high (mixed) settings and looks awesome (if im not mistaken and remember the fps right, sorry if it is wrong), like a new title from this year. For games like Overwatch I dial down as much as needed to get 165hz. Some games even don't go higher than 60fps/hz, like Tekken 7. And Playerunkown's Battleground is not very good optimized and to get 80fps and not to go low on quality settings, I set it to 1080p, which looks slightly blurrier on my monitor, but only if I make a comparison. Never forget that option to be able to set lower resolution.
But my experience is with G-Sync enabled. G-Sync can make the monitor 150-200 Euro/Dollar more expensive, but its worth in my opinion. That way my montor is not fixed to a specific hz while gaming. If it goes below 60fps, the monitor change the displayrate (hz) and adapt it (thats why G-Sync and FreeSync are called Adaptive Sync). The good thing is, you don't have the input lag like you would get with V-Sync, but you also don't have tearing if you would set off V-Sync. So, G-Sync is best to both worlds. Without it, I could not play my games at such high settings and high fps, as I would enable V-Sync at 60hz, because my system can't hold 165fps whole time.
Hope this wasn't confusing answer. Just ask more if you want to know something.