This has gone into fairytales territory lately, with people fighting (and loosing at it) vsync lag on 240Hz panels. I mean, I don't really notice any lag on my 60Hz non-gaming one (albeit it's rather fast in gaming mode) so it's kinda hard for me to believe that a lot of people would even notice lag at 144Hz, let alone 240.
Anecdotal experience: mucked around with various settings inside and outside the game.
It seems like the input lag isn't noticeable at all with in-game v-sync on, on my 60 Hz monitor, but with a note that the NVIDIA Control Panel settings have the game's max rendered frames set to 1. The game's mouse cursor will feel a bit heavy in the lobby, but it's responsive in an actual game.
It also seems like setting all settings to their maxed out equivalents outside of textures, shadow resolution, and baking the static shadows (disabled) is doable on a GTX 970 in my experience. (Maxing out the texture and resolution settings induces momentary hitches in gameplay.)
I did flip on the shader cache (I'm willing to trade initial load times for less in-game stuttering as I'm on an SSD), as well as making player weapon shadowing always turned on. I don't like graphical effects that disable themselves.
Does the game run poorly on systems with just 8 GB of RAM, or on a HDD install? I have a friend that seems to be having severe stuttering with a 970 and a 4.8 GHz i5-4690K, but just 8 GB of DDR3-1600 RAM and a normal HDD. (I have a stock i5-4590.)
NB: if you prefer using Fast Sync, the best setting for the game seem to Medium everything, all extra features but shadow baking turned on, weapon shadows auto on, to make it manage 120 FPS most of the time.