Thanks for the insight.
AFAIK the USB-C port can not be used for wired connection.
The MX master seems to be internally hobbled at 125Hz(would love to be proved wrong on this). Online mouse-polling check-sites show it polling at around 120-130Hz.
I'll keep my previous Rival 300 plugged in, and switch to it where necessary. (Also just found out about rivalcfg to try and get some more tweaks from that mouse.)
Thanks for your work on this project. I'll keep playing around with it.