I do test wayland from time to time on my unstable install, and also test the new things in KDE Plasma 5.25 - for me, many things do not work on it as work on 5.24.6 on testing branch install. Also very dependent to have my workflow flawless.
As for the
Depending on what GPU you have, there are ways to set the values different for each monitor
Also there is via xrandr possible to get different refresh rate for each monitor https://linuxconfig.org/how-to-configure-your-monitors-with-xrandr-in-linux, or as described here Variable refresh rate - ArchWiki