I've recently upgraded my home internet from 100MB FTTP to 500mb.  I very quickly realised that my P9 DECO system wouldn't provide the download speeds i was being provided from my internet.  So i brought DECO XE75 PRO.  

My home set is as follows.  

Internet comes into house via the ONT provided by OPENREACH.  At first i had LAN from ONT to the EE router, then into my DECO system.  But was finding although my wifi signal was throughout the house.  I only got the full benefit of 500mb download if i connected to the WIFI coming from the EE hub whilst sat in the same room.  The WIFI speeds from DECO across the rest of the house was similiar to when i was on 100mb on my P9 system. 

So i binned the EE ROUTER and having brought XE75 PRO connected the ONT straight into this and found the settings to have the DECO manage all the settings EE hub normally does.  The speeds were definitely much better.  In the same room as the main router and ONT i get between 400-480 on wifi on my old Iphone 12.  

I have another DECO in the kitchen which was connected via an ethernet cable from a Powerline TP kit PA8030P 13000mps.  

I then have another DECO in the back bedroom on the first floor of the house, connected via WIFI.  

I don't have any WIFI 6 devices, so am currently using this as the dedicated backhaul.  

The issue being I'm only getting about 200>250mb download in the kitchen and back bedroom on wifi.   

I was expecting the kitchen DECO to be able to put out similiar wifi speeds to that of the main unit on the basis its connected via ethernet.  I've considered this might be the bottleneck but can't establish why.  I've downloaded the PLC software and see the connection between the powerline adapters is about 670mb.  oh forgot to mention, i've connected the powerline adapater from my main DECO by a CAT 8 cable and same other end, considering it could be a cable speed issue but is still the same.  

As part of being able to use the PLC software, i've connected direct to powerline adapter via LAN on my laptop and was only getting just over mid 200mb.  So Powerline would appear to be the bottle next for somereason.  Even though software shows adapaters connected at around 670mb.  

So i thought i would try without the powerline LAN connection into the DECO.  Having the XE75 connect to each unit via WIFI. Results being LAPTOP connected to kitchen DECO, via LAN 480mb.  Wifi on laptop 400mb.  

I would have thought connecting the kitchen DECO to the main DECO via powerline adapter and therefore LAN would provide a faster more reliable base connection for the KITCHEN DECO to provide the best WIFI download possible.  

Am i missing something with connecting my DECO's via LAN through the POWERLINE adapter?  ( I know the best, would be LAN straight from MAIN DECO to KITCHEN one, but this isn't possible, so was thinking POWERLINE was next best step).  Or is connecting the DECO's via WIFI the best way to go and leave it as it currently is now and this will provide the best download speeds over WIFI?  

I'm keen to get the most out of my FTTP broadband, after all paying for the 500mb download and whilst i know i won't get the full 500 all over the house via Wifi.  Want to try and get at least 400mb around most of the house.  Any help / suggestions would be grateful.  Tried to look up getting a professional company to come out and try and suggest best WIFI set up, but not many around and one of only ones i found, didn't even reply to my message.  Thanks in advance.