Another Gnome user here (with Nvidia Graphics on Xorg). The Update itself runs smoothly without any breaks. So great job! 
The Adwaita-maia theme needs some smaller updates, e.g. the corners of the background of the dock looks weird, but that’s only minor issues.
The only issue I have so far is the performance within non GTK applications. The rendering inside those applications becomes some kind of choppy and laggy, especially when scrolling. For example, the Firefox browser or any electron based app. But maybe this issue is because of the new Nvidia driver (470.42.01).
Edit: Yes, it seems Nvidia is the evil (of course they are 
): https://forum.manjaro.org/t/opengl-and-opencl-not-working-anymore-after-ugrading-to-nvidia-470-42-01/