@Nidget 

As a rule, newer versions of WiFi protocol offer faster speeds, but they travel shorter distance and not good at penetrating brick and stone walls.

Ideally, you should bring Ethernet (or coaxial) cable to each room where you need strong WiFi. Wired Deco unit withing that room can provide fast speeds. How fast speeds you can get- obviously not faster than your Internet link.

WiFi signal that goes through thick wall will fade faster for newer WiFi protocols. Which means, through the wall WiFi connection will most likely be established over WiFi 2.4GHz, less likely over faster WiFi5 and unlikely over WiFi6, WiFi 6e and WiFi 7.

Each Deco model (as of now) supports WiFi 2.4GHz, but if you need WiFi signal going through walls you will be wasting money buying WiFi7 capable hardware. Deco with WiFi6 and even WiFi5 will do same in same scenario.

XE75Pro difference from XE75 is 2.5GBps Ethernet port. To make use of it, you must have home LAN (wired network) capable of supporting 2.5GBps and also Internet link speed exceeding Gigabit. Otherwise, you will be paying premium for hardware capabilities of Deco you can't use.

  @Alexandre. 

Thanks,

3 primary Deco's are currently wired with Cat6 via a central switch, (Living Room, kitchen diner and top of stairs) to act as a 'backbone', + office room too for wfh. The remaining 2 M9+'s are wireless satellites to improve connectivity.

I guess the question regarding end point is, for coverage and future upgrade, am I better with 5x XE75 variants (3 wired, 2 not) or 3x BE63 (wired) and 2x XE75 (satellite)?

  @Nidget 

Based on my experience with Deco mesh, my personal preference would be to run it on Deco units all supporting same set of WiFi protocols, ideally same Deco model. 

That makes Deco mesh behavior more predictable when it comes to device roaming between Deco units, also makes troubleshooting much easier.

For that reason, my recommendation would be "5x XE75 variants" and not "3x BE63 and 2x XE75."