It will be an individual thing how significant the difference between 75, 80 and 90 Hz will be. Some will not be sensitive to it at all while others will be. And then there are sceptics who fear that the FoV increase will demand a higher refresh rate to achieve equal comfort - for the moment I believe this is speculation and has not been confirmed.
As I mentioned in another post, I did not notice any difference between the V2 (apparently @80 Hz) to my Rift/Vive (@90 Hz) when trying Fruit Ninja, not even in the parts where I shook my head wildly. But of course the scenario was static in the sense that I was not moving within the scene.
As ever in this forum - let's wait and see.