I have both an iPad Air 2 (60Hz) and an iPad Pro 10.5 (ProMotion 120Hz). (I wanted to trade in my Air 2 but saw it wasn't worth much so decided to keep it)
Scrolling is smoother on the latter, but it wasn't appreciable enough that the iPad Air 2 looked bad in comparison. I could continue using the Air 2 without any FOMO.
Maybe it makes more of a difference for artists? (Pencil users)
It is indeed a stark difference in latency - I posted this earlier but it's worth repeating:
If you are using a pencil I understand the difference is dramatic. Excellent thoughts from Serenity Caldwell who loves to draw: https://www.imore.com/promotion
When LCD TVs first came out I thought people were being overly dramatic with the whole motion blur thing - until I went looking for it. And then I saw it - every time a scene was still, it was in perfect clarity - the the camera panned and everything went fuzzy. Once I saw that effect I couldn't unsee it. 120Hz scrolling is the same for me too.
Ignorance is indeed bliss :)