Just spent some time with the iPhone X and an Ipad Pro. My conclusion is that the refresh rate on the oled is more related to the pwm than the refresh rate on the led/non-oled backlight. The ipad pro 120hz didnt really feel any different that 60hz. Think the LED backlight is doing the same thing it does. Did look smoother for sure.
However, the iphone oled is refreshing at 60hz along with the digital/lcd info. Saw a video of the 60hz PWM on the iphone x.
I could use the iphone X for a little bit at half to full brightness, but it was not pleasant. Turned it down below 25% and it was nightmare status.
So to wrap this up: occulus uses 90hz oled display that feels fine for my eyes. It also uses Low Persistancy black frames to clear the previous frame. So that might also be adding some type of added comfort element to the equation. Phone oleds currently on the market are 60hz. Some of the new phones can enter Low Persistancy mode, however with the slower 60hz the inserted blank screens will appear as flickering.
So I am hoping my holy grail is 90hz or higher oled display.