The memory speed and ability to overclock your CPU are the main two benefits of going to Z390.
Going from 2666Mhz to 3200Mhz RAM speed will indeed speed up certain tasks, but it depends on what you do. This video shows a range of different applications at different speeds:
Long story short, certain applications see no difference. But in the ones that do, mainly the fps 'lows' will increase (e.g. it will lessen the stuttering).