Well, I got 900 mbps fibre installed and the ethernet speed was fine at 925 mbps up/down.
However wifi was much lower at 400 mbps up/down.
I checked all my cables were cat 6 or above.
No matter what settings I changed, I could not improve the wifi.
The wifi router I have only has two bands 2.4 GHZ and 5 GHZ and in the end, my specs indicated they are good for 866 mbps but I could not get that no matter what. I bought a cheapish wifi 6 router and daisy chained it to main router by ethernet lan to lan, disabled dhcp on new router, gave new router a static ip address, and Boom - over 800 mbps up/down. I then disabled wifi on main router and all is fine.
I guess I will never get the full 900 mbps with wifi as it always carries a bit of wifi performance overhead, but 800 mbps is pretty damn good. for a domestic consumer.