I have this same issue with CS GO because I can push something stupid like 250 plus FPS. Even with GSync on, it still causes lag and issues. If I go into CS GO console and run the command max_fps 144. I have zero issues what so ever with GSync remaning on or off. However, this is a CSGO issue, not a gsync or vsync issue, as I'll play in other games with higher FPS then my monitor supports in herts, and it works fine and GSync does its thing.
I don't really think CS GO is a good example here.
But yes, in some games performing very high FPS, it matters.
I'd never advise anyting below a 144 herts monitor, there is no reason too anymore. That was the old standard. If you get a 144 hert monitor and can't reach that in FPS, you can simple...