@David-TP

Thanks for your answer.

I understand that wireless/wifi backhaul will always be somewhat lossy in terms of performance but wired backhaul is not a possibility for me.

My focus with a fairly large (6bed) house with all internal walls being brick is what range I will get from each model. So I suppose my question is really do any of the following have any better range if using wireless backhaul - given that the advantage of faster wifi standards such as 6, 6E and 7 is not really relevant when only having to pass through a maximum rate of 150mb:

X50

X60

X95

XE75

XE200

For example, if someone could tell me that with a 150mb internet speed the XE75 will have a higher throughput to another node that is 50ft and two brick walls away than the X50, then it is worth the extra money to me. Similarly if the XE200 is better than the XE75 in the same respect then it is worth it over the XE75.   

Perhaps the range on all devices (when your internet speed isnt very fast) is essentially the same - especially as they are all limited by the same legal limits on the strength of the signal they can produce. However, maybe higher up models have better beamforming or directionality to other nodes - or triband is better than dual band even for 150mbs, etc.

  @GadgetObsessed 

I can narrow down Deco models from your list.

1. It does make sense to have all units in WiFi mesh support same WiFi protocols. X50-5G is WiFi 6, meaning WiFi 6E and WiFi 7 Deco models won't be a good addition to it. They'll work with X50-5G, but may bring some subtle issues in the process;

2. Any new and faster WiFi protocol is more sensitive to obstacles such as brick walls. Buying more expensive units with faster protocols may not bring any benefits, as their speed of wireless backhaul will be severely limited by brick walls. That is another reason not to invest in more than Main Deco delivers, which is WiF6 in your case;

3. Tri-band is always better than dual-band, but you will only see its benefit if Main Deco supports tri-band. X50-5G does not. Spending extra on Satellite Decos that have tri-band capability without Main Deco supporting it will be waste of money.

That narrows your list to two options:

X50

X60

There is also X55, which is very similar to X50 and should be considered. In some regions, TP-Link sells both X50 and X55, one on sale another not. Makes sense to get one that is sold for less, because otherwise they are practically identical.

It now comes to choosing between X50/X55 and X60. If you need three Ethernet ports on Satellite Deco, because you have number of devices you can wire to them, choose X50/X55. 

Otherwise, X60 might slightly be better with signal strength, but no guarantees you'll notice the difference.

Also, if you plan star type of deployment, where all Satellite Deco connect to Main Deco, it does not matter if you choose X60, X55 or X50. In case you plan for chaining Satellite Deco through each other to Main Deco, I'd suggest X50/X55. Due to specifics of X60 submodels, not every X60 supports daisy chaining feature. 

  @Alexandre. 

In the end I got the XE75 Pro.

You persuaded me that I should run a cable from the X50-5G to the first XE75 and the other two XE75s connect to that wirelessly.

The cable is just run around the edge of a room and under a door at the m0oment so is a bit unsightly. Sill have to see how I can hide it better.