You can add a frame cap in the Nvidia Control Panel-
If you do it in the global settings, it’ll apply it to all applications. (That would only negatively affect benchmarks)
For the most part none really.
For some. A dip from 90 to 70 when your monitor is 60Hz is unnoticeable, if you locked it at 60 then a dip from 60 to something lower is noticeable.
Screen tearing and instability in frame rate ruins the experience imo. I’d rather 60 solid than 70-80 fluctuation. That being said Just Get A Gsync (TM)