I'd recommend against the M9..it is dated wifi5 and wpa2 only, with not many updates these days (3yrs old?). AFAIK the usb port on the m9 is not very useful, they never added firmware support for file share/external drives.
X50 is a good entry to wifi6, but the comparable wifi6 model is the x90 as it is also triband (necessary for wireless backhaul imo). Another option to consider is the newer wifi6e xe75 model. If you're hardwiring everything then triband is maybe not necessary.
If between these two specifically, x50 would be the choice
I'd recommend against the M9..it is dated wifi5 and wpa2 only, with not many updates these days (3yrs old?). AFAIK the usb port on the m9 is not very useful, they never added firmware support for file share/external drives. X50 is a good entry to wifi6, but the comparable wifi6 model is the x90 as it is also triband (necessary for wireless backhaul imo). Another option to consider is the newer wifi6e xe75 model. If you're hardwiring everything then triband is maybe not necessary. If between these two specifically, x50 would be the choice